V4L/DVB (7103): make stk_camera_cleanup() static

stk_camera_cleanup() can become 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>