media: ivtv: don't allow negative resolutions as module parameters

This driver takes "osd_xres" and "osd_yres" as module parameters and
caps the upper bounds but it doesn't cap the lower bounds.  Obviously
the admin is not going to enter negative resolutions but the possibility
makes static analysis more difficult.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>