Inside vaapi.c the function vlc_va_Release() only has a VASurfaceID when
the ffmpeg Frame buffer is no longer needed. The VA Connection struct works
with vlc_va_surface_t pointer, thus a way is needed to find the surface
which belongs to this VASurfaceID. Initially this was coded inside the
vlc_va_Release() functionality, but that exposes details that should be
remain inside va.c file.