media: cx25840: set_fmt operation should clamp out-of-range picture sizes

According to V4L2 API set_fmt subdev operation should not return an error
on out-of-range picture sizes, the values should be clamped instead to the
supported range.

The cx25840 datasheet says that the chip is capable of scaling down the
picture width and height, respectively, 16 and 8 times.
These values agree with what the old implementation enforced.

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>