V4L/DVB (4375): Eliminate hardcoded limits in VIDIOC_[S|TRY]_FMT for pvrusb2

The pvrusb2 implementation for VIDIOC_[S|TRY]_FMT was hardcoding
limits on the range for allowed resolution, but it would be much
better if we instead just queried the internal control for these
values.  This then opens the door for the driver to adjust these
limits based on the detected hardware.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>