V4L/DVB (5026): Pvrusb2-hdw kfree cleanup

Removes redundant argument check for kfree().

Signed-off-by: Mariusz Kozlowski <m.kozlowski@tuxland.pl>
Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>