V4L/DVB (7704): pvrusb2: Fix slop involving use of struct which might not be defined

V4L/DVB (7704): pvrusb2: Fix slop involving use of struct which might not be defined

When the DVB interface is not compiled, the pvr2_dvb_props struct is
not available - so it really should be ifdef'ed out as well.  This
didn't cause an error because in this context its usage was as an
opaque pointer.  But it really shouldn't be present at all if DVB is
not enabled.

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