[media] pvrusb2: For querystd, start with list of hardware-supported standards

The V4L querystd implementation appears to want to narrow down the
list of available standards by starting with a hardware-supported list
and then attempting to detect which among those are actually
available.  Prior to this change in the pvrusb2 driver we started with
all possible standards.  With this change in place we instead narrow
to just the standards that we know the hardware can actually support.
For example, this removes the ATSC standards from the list if we
aren't dealing with a hybrid device...

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