media: coda: fix mpeg2 sequence number handling

Sequence number handling assumed that the BIT processor frame number
starts counting at 1, but this is not true for the MPEG-2 decoder,
which starts at 0. Fix the sequence counter offset detection to handle
this.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>