[media] pvrusb2: width and height maximum values

pvrusb2: The origin of the capability bounds rectangle may differ from
(left=0,top=0) so the calculation should use absolute coordinates,
here below, or use relative coordinates like
cropl_val-cap->bounds.left and cropt_val-cap->bounds.top.

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