[media] media: rcar-vin: fix bug in scaling

It was not possible to scale beyond the image size of the video source
limitation. The output frame would be bigger but the captured image was
limited to the size of the video source.

The error was that the crop boundary was set after the requested frame
size and not the video source size. This patch breaks out the resetting
of the crop, compose and format to separate functions so the error wont
creep back.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>