[media] hdpvr: improve error handling

get_video_info() should never return EFAULT, instead it should return
the low-level usb_control_msg() error. Add a valid field to the hdpvr_video_info
struct so the driver can easily check if a valid format was detected.
Whenever get_video_info is called and it returns an error (e.g. usb_control_msg
failed), then return that error to userspace as well.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>