[media] mt9v022: set y_skip_top field to zero as default

Set "y_skip_top" to zero and revise comment as I do not see this line
corruption on two different mt9v022 setups. The first read-out line
is perfectly fine. Add mt9v022 platform data configuring y_skip_top
for platforms that have issues with the first read-out line. Set
y_skip_top to 1 for pcm990 board.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Acked-by: Eric Miao <eric.y.miao@gmail.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>