V4L/DVB (4287): Pvrusb2/: possible cleanups

This patch contains the following possible cleanups:
- make needlessly global code static
- #if 0 unused global functions

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>