bug#38435: BTRFS open_ctree failed

[raingloom]

This is what I get after a recent `guix system reconfigure` :
Scanning for Btrfs filesystems
[    2.342790] BTRFS error (device sda1): open_ctree failed

Previous profiles work, I haven't modified anything about my config.scm
between them.

Full output from kernel (taken by booting it from QEMU and redirecting
ttyS0 to stdio):
```
qemu-system-x86_64 -enable-kvm -cpu host -smp 2 -hda /dev/sda -m 1G
-serial stdio WARNING: Image format was not specified for '/dev/sda'
and probing guessed raw. Automatically detecting the format is
dangerous for raw images, write operations on block 0 will be
restricted. Specify the 'raw' format explicitly to remove the
restrictions. GC Warning: pthread_getattr_np or pthread_attr_getstack
failed for main thread GC Warning: Couldn't read /proc/stat Welcome,
this is GNU's early boot Guile. Use '--repl' for an initrd REPL.

loading kernel modules...
Scanning for Btrfs filesystems
[    2.342790] BTRFS error (device sda1): open_ctree failed
ERROR: In procedure mount:
In procedure mount: Invalid argument

Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
GNU Guile 2.2.6
Copyright (C) 1995-2019 Free Software Foundation, Inc.

Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
This program is free software, and you are welcome to redistribute it
under certain conditions; type `,show c' for details.

Enter `,help' for help.
scheme@(guile-user)> ,bt
In gnu/build/linux-boot.scm:
   533:14  2 (_)
    387:8  1 (mount-root-file-system _ _ #:volatile-root? _ #:options …)
In unknown file:
           0 (mount "/dev/sda1" "/root" "btrfs" 0 "lazytime,compress")
scheme@(guile-user)> ,q  
[   42.345826] Kernel panic - not syncing: Attempted to kill init!
```
(rest of stack trace snipped for brevity's sake)

output of `guix describe` as root:
```
Generation 26   Nov 29 2019 21:22:41    (current)
  nonguix 2df6923
    repository URL: https://gitlab.com/nonguix/nonguix.git
    branch: master
    commit: 2df692312100ac5bea9ed8e8bf0032e6db100e91
  guix dac7928
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: dac7928d502d9ba4fc6a9621e5b2b15019d92d5b
```

Contents of /etc/profile.scm:

```
(define use-proprietary-crap? #f)

(use-modules (gnu)
             (gnu system nss)
             (gnu packages shells)
             (gnu packages package-management)
             (gnu packages gnome))

(if use-proprietary-crap?
    (use-modules (nongnu packages linux))
    (use-modules (gnu packages linux)))

(use-service-modules desktop ssh nix)
(use-package-modules
 bootloaders
 certs
 ratpoison
 suckless
 wm)

(operating-system
  (host-name "bingobongo")
  (timezone "Europe/Budapest")
  (locale "en_US.utf8")
  (kernel
   (if use-proprietary-crap?
       linux
       linux-libre))
  (firmware (append
             (if use-proprietary-crap?
                 (list iwlwifi-firmware)
                 '())
             %base-firmware))

  ;; Use the UEFI variant of GRUB with the EFI System
  ;; Partition mounted on /boot/efi.
  (bootloader (bootloader-configuration
                (bootloader grub-bootloader)
                (target "/dev/sda")))

  ;; Assume the target root file system is labelled "my-root",
  ;; and the EFI System Partition has UUID 1234-ABCD.
  (file-systems (cons* (file-system
                         (device (file-system-label "GUIX"))
                         (mount-point "/")
                         (options "lazytime,compress")
                         (type "btrfs"))
                       ;(file-system
                       ;  (device (uuid "1234-ABCD" 'fat))
                       ;  (mount-point "/boot/efi")
                       ;  (type "vfat"))
                       %base-file-systems))

  (users (append (list
                  (user-account
                   (name "raingloom")
                   (comment "your friendly localhost admin")
                   (group "users")
                   (shell "/run/current-system/profile/bin/zsh")
                   (supplementary-groups '("wheel" "netdev" "audio"
  "video" "kvm")) (home-directory "/home/raingloom")))
               %base-user-accounts))

  ;; Add a bunch of window managers; we can choose one at
  ;; the log-in screen with F1.
  (packages (cons* i3-wm i3status dmenu ;window managers
                   nss-certs            ;for HTTPS access
                   zsh                  ;nicer login shell
                   gvfs
                   nix
                   gnome
                   orca
                   %base-packages))

  ;; Use the "desktop" services, which include the X11
  ;; log-in service, networking with NetworkManager, and more.
  (services
   (append (list (service nix-service-type) (service
  openssh-service-type (openssh-configuration (x11-forwarding? #t))))
  (modify-services %desktop-services
            (elogind-service-type config =>
                                  (elogind-configuration
                                   (inherit config)
                                   (handle-lid-switch 'ignore))))))

  ;; Allow resolution of '.local' host names with mDNS.
  (name-service-switch %mdns-host-lookup-nss))
```