multimedia/libva: unbreak DRM backend in some cases

$ vainfo
error: XDG_RUNTIME_DIR not set in the environment.
error: can't connect to X server!
vaInitialize failed with error code 1 (operation failed),exit

$ ls -lL /dev/dri
total 0
crw-rw---- 1 root video 0x188 Mar 30 17:28 card0
crw-rw---- 1 root video 0x208 Mar 30 17:28 renderD128

$ echo $((0x208 & 0x80))
0

Reported by: 김종성 (via private mail)