[media] au0828: Cancel stream-restart operation if frontend is disconnected

If the tuner is already disconnected, It is meaningless to go on doing the
stream-restart operation, It is better to cancel this operation.
Signed-off-by: NChangbing Xiong <cb.xiong@samsung.com>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/au0828/au0828-dvb.c

@@ -471,6 +471,8 @@ void au0828_dvb_unregister(struct au0828_dev *dev)
 	if (dvb->frontend == NULL)
 		return;
 
+	cancel_work_sync(&dev->restart_streaming);
+
 	dvb_net_release(&dvb->net);
 	dvb->demux.dmx.remove_frontend(&dvb->demux.dmx, &dvb->fe_mem);
 	dvb->demux.dmx.remove_frontend(&dvb->demux.dmx, &dvb->fe_hw);