[media] cx231xx: declare static functions as such

[media] cx231xx: declare static functions as such

drivers/media/video/cx23885/built-in.o: In function `mc417_memory_write':
/home/v4l/v4l/patchwork/drivers/media/video/cx23885/cx23885-417.c:482: multiple definition of `mc417_memory_write'
drivers/media/video/cx231xx/built-in.o:/home/v4l/v4l/patchwork/drivers/media/video/cx231xx/cx231xx-417.c:477: first defined here
drivers/media/video/cx23885/built-in.o: In function `mc417_gpio_set':
/home/v4l/v4l/patchwork/drivers/media/video/cx23885/cx23885-417.c:636: multiple definition of `mc417_gpio_set'
drivers/media/video/cx231xx/built-in.o:/home/v4l/v4l/patchwork/drivers/media/video/cx231xx/cx231xx-417.c:615: first defined here
drivers/media/video/cx23885/built-in.o: In function `mc417_gpio_enable':
/home/v4l/v4l/patchwork/drivers/media/video/cx23885/cx23885-417.c:656: multiple definition of `mc417_gpio_enable'
drivers/media/video/cx231xx/built-in.o:/home/v4l/v4l/patchwork/drivers/media/video/cx231xx/cx231xx-417.c:635: first defined here
drivers/media/video/cx23885/built-in.o: In function `mc417_memory_read':
/home/v4l/v4l/patchwork/drivers/media/video/cx23885/cx23885-417.c:546: multiple definition of `mc417_memory_read'
drivers/media/video/cx231xx/built-in.o:/home/v4l/v4l/patchwork/drivers/media/video/cx231xx/cx231xx-417.c:541: first defined here
drivers/media/video/cx23885/built-in.o: In function `mc417_gpio_clear':
/home/v4l/v4l/patchwork/drivers/media/video/cx23885/cx23885-417.c:646: multiple definition of `mc417_gpio_clear'
drivers/media/video/cx231xx/built-in.o:/home/v4l/v4l/patchwork/drivers/media/video/cx231xx/cx231xx-417.c:625: first defined here
drivers/media/video/cx23885/built-in.o: In function `mc417_register_read':
/home/v4l/v4l/patchwork/drivers/media/video/cx23885/cx23885-417.c:388: multiple definition of `mc417_register_read'
drivers/media/video/cx231xx/built-in.o:/home/v4l/v4l/patchwork/drivers/media/video/cx231xx/cx231xx-417.c:401: first defined here
drivers/media/video/cx23885/built-in.o: In function `mc417_register_write':
/home/v4l/v4l/patchwork/drivers/media/video/cx23885/cx23885-417.c:324: multiple definition of `mc417_register_write'
drivers/media/video/cx231xx/built-in.o:/home/v4l/v4l/patchwork/drivers/media/video/cx231xx/cx231xx-417.c:343: first defined here

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>