V4L/DVB (12526): ov772x: do not use scaling for cropping

OV772x sensors cannot crop, they only support two fixed formats: VGA and QVGA.
We should not change the format when requested to crop, only S_FMT can do this.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>