media: adv7842: configure all pads

Only the first pad was configured, but there are 4. This causes
set_fmt to fail with -EINVAL since the passed pad is > 0.

Configure all three sink pads and the source pad.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>