V4L/DVB (4372): Clean up some post mpeg-controls issues in pvrusb2

Fix a few miscellaneous issues in the pvrusb2 driver related to use of
the new mpeg controls.  This also should fix problems involving
update of the saa7115 / cx25840 configuration as control changes are made.

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