vulkan/video: Do byte-alignment when building a h264 slice header

Fixes: ff8de6190 ("vulkan/video: adds a bitstream writer of h264 slice header")
Closes: mesa/mesa#12835

Signed-off-by: Hyunjun Ko <zzoon@igalia.com>
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34094>
1 file changed