Fix out of tree builds
Fix out of tree builds

Prefix the libva.sym file or it will not be found when doing out of
tree builds.

Spotted by 'make distcheck'.

Signed-off-by: Emil Velikov <4c996f2f093ddd0585a556460b4cc3ba555546ef@gmail.com>

chenxianqin/vaapi-libva,01org/iotg-lin-gfx-libva,chenxianqin/vaapi-libva,01org/iotg-lin-gfx-libva,01org/libva-cros,zzhhui/libva,chenxianqin/vaapi-libva,zzhhui/libva,01org/libva-cros,01org/iotg-lin-gfx-libva,01org/libva-cros,gbeauchesne/libva,gbeauchesne/libva,gbeauchesne/libva,zzhhui/libva