radio tea5764, si4713: get rid of warning: no previous prototype

drivers/media/radio/radio-tea5764.c:148:5: warning: no previous prototype for 'tea5764_i2c_read' [-Wmissing-prototypes]
drivers/media/radio/radio-tea5764.c:168:5: warning: no previous prototype for 'tea5764_i2c_write' [-Wmissing-prototypes]
drivers/media/radio/si4713-i2c.c:1772:6: warning: no previous prototype for 'si4713_ioctl' [-Wmissing-prototypes]

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