[media] pvrusb2: Stop statically initializing reserved struct fields to zero

In any statically initialized data structure, the compiler is going to
zero any part which is not already explicitly initialized.  While we
can take that knowledge overboard and simply avoid initializing
anything that needs to be zero, it's at least a good idea not to
bother zeroing parts that we don't otherwise care about - like
"reserved" fields which may change in the future.  Avoiding
initialization of those fields now also avoids possible conflict down
the road.

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