media: v4l2-ctrls: Fix H264 SEPARATE_COLOUR_PLANE check

The `separate_colour_plane_flag` element is only present in the SPS if
`chroma_format_idc == 3`, so the corresponding flag should be disabled
whenever that is not the case and not just on profiles where
`chroma_format_idc` is not present.

Fixes: b32e4850 ("media: controls: Validate H264 stateless controls")
Signed-off-by: James Cowgill <james.cowgill@blaize.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>