[media] mxl111sf: missing return values validation

Return values of mxl111sf_enable_usb_output and mxl1x1sf_top_master_ctrl
are not validated.

Signed-off-by: Insu Yun <wuninsu@gmail.com>
Reviewed-by: Michael Ira Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>