V4L/DVB (8440): gspca: Makes some needlessly global functions static.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>