media: cedrus: h264: Properly configure reference field

When interlaced H264 content is being decoded, references must indicate
which field is being referenced. Currently this was done by checking
capture buffer flags. However, that is not correct because capture
buffer may hold both fields.

Fix this by checking newly introduced flags in reference lists.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>