[media] vp702x: get rid of warning: no previous prototype

drivers/media/usb/dvb-usb/vp702x.c:70:5: warning: no previous prototype for 'vp702x_usb_out_op_unlocked' [-Wmissing-prototypes]
drivers/media/usb/dvb-usb/vp702x.c:89:5: warning: no previous prototype for 'vp702x_usb_out_op' [-Wmissing-prototypes]

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