bug#48868: VLC cant find libvdpau_radeonsi.so when playing video

[Brendan Tildesley]

The file exists at 
/gnu/store/mwcgqw9ggi02p8mhzac8cg0x671j7wd1-mesa-20.2.4/lib/vdpau/libvdpau_radeonsi.so
but it doesn't seem to be found (by libva?). 
Videos still play. Probably requires a Radeon card to reproduce.
I got confused trying to figure out where exactly its loaded.

libva info: VA-API version 1.10.0
libva info: Trying to open 
/gnu/store/gvncg7gzdzjx0gvyi4sm02m7qgnsmx5q-mesa-20.2.4/lib/dri/radeonsi_drv_video.so
libva info: Found init function __vaDriverInit_1_10
libva info: va_openDriver() returns 0
[00007f6928001f80] glconv_vaapi_x11 gl error: vaDeriveImage: operation failed
[00007f69240ba3a0] main video output error: video output creation failed
[00007f69e8c929f0] main decoder error: failed to create video output
Failed to open VDPAU backend libvdpau_radeonsi.so: cannot open shared object 
file: No such file or directory
Failed to open VDPAU backend libvdpau_radeonsi.so: cannot open shared object 
file: No such file or directory