V4L/DVB (5086): Pvrusb2: Fix missing break statement on VIDIOC_S_TUNER

The lack of a break statement in the handling of VIDIOC_S_TUNER caused
errors to result.  Fixed.

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