V4L/DVB (7104): stk-sensor.c: make 2 functions static

This patch makes the following needlessly global functions static:
- stk_sensor_outb()
- stk_sensor_inb()

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>