V4L/DVB (4147): Drivers/media/video/pwc/: make code static

This patch makes the following needlessly global code static:
- pwc-ctrl.c: pwc_get_leds()
- pwc_preferred_compression

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