media: am437x-vpfe: Fix missing first line

Previous generation of this driver were hard coded to handle
encoder/decoder where the first line never contains any data and
was therefore always skipped, however when dealing with actual
camera sensors the first line is always present.

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Jyri Sarha <jsarha@ti.com>
Acked-by: Lad Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>