mxl111sf: Fix compile when CONFIG_DVB_USB_MXL111SF is unset

commit 13e1b87c986100169b0695aeb26970943665eda9 upstream.

Fix the following build error:

drivers/media/usb/dvb-usb-v2/
mxl111sf-tuner.h:72:9: error: expected ‘;’, ‘,’ or ‘)’ before ‘struct’
         struct mxl111sf_tuner_config *cfg)

Signed-off-by: Dave Jones <davej@fedoraproject.org>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>