media: vimc: Don't iterate over single pad

The .init_state() operations of the debayer and sensor entities iterate
over the entity's pads. In practice, the iteration covers a single pad
only. Access the pad directly and remove the loops.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>