[media] V4L: sh_mobile_ceu_camera: don't try to improve client scaling, if perfect

If the client has managed to configure the precise output format,
we don't have to try to further improve it.

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