V4L/DVB (7238): make stk_camera_{suspend,resume}() static

This patch makes the needlessly global stk_camera_{suspend,resume}()
static.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Jaime Velasco Juan <jsagarribay@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>