vdpau: remove bogus assert

vdpau: remove bogus assert

The assert introduced by 24f2b0a8560 triggers when an application
requests a chroma_type that's different to the one from the
PIPE_VIDEO_CAP_PREFERED_FORMAT (before this change the chroma_type
was set but ignored).

So restore this behavior and ignore the chroma_type.

Reported-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Fixes: 24f2b0a8560 ("gallium/video: remove pipe_video_buffer.chroma_format")
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4104>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4104>