[media] V4L: sh_mobile_ceu_camera: don't fail TRY_FMT

VIDIOC_TRY_FMT shouldn't fail if the user requests an unsupported pixel
format. Instead the driver should replace it with a supported one. Fix the
sh_mobile_ceu_camera driver accordingly.

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