[media] use a function for DVB media controller register

This is really a simple function, but using it avoids to have
if's inside the drivers.

Also, the kABI becomes a little more clearer.

This shouldn't generate any overhead, and the type check
will happen when compiling with MC DVB enabled.

So, let's do it.

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/common/siano/smsdvb-main.c

···
 		pr_err("dvb_register_adapter() failed %d\n", rc);
 		goto adapter_error;
 	}
-#ifdef CONFIG_MEDIA_CONTROLLER_DVB
-	client->adapter.mdev = coredev->media_dev;
-#endif
+	dvb_register_media_controller(&client->adapter, coredev->media_dev);
 
 	/* init dvb demux */
 	client->demux.dmx.capabilities = DMX_TS_FILTERING;

drivers/media/dvb-core/dvbdev.h

···
 
 #ifdef CONFIG_MEDIA_CONTROLLER_DVB
 void dvb_create_media_graph(struct dvb_adapter *adap);
+static inline void dvb_register_media_controller(struct dvb_adapter *adap,
+						 struct media_device *mdev)
+{
+	adap->mdev = mdev;
+}
+
 #else
 static inline void dvb_create_media_graph(struct dvb_adapter *adap) {}
+#define dvb_register_media_controller(a, b) {}
 #endif
 
 extern int dvb_generic_open (struct inode *inode, struct file *file);

drivers/media/usb/cx231xx/cx231xx-dvb.c

···
 		       dev->name, result);
 		goto fail_adapter;
 	}
-#ifdef CONFIG_MEDIA_CONTROLLER_DVB
-	dvb->adapter.mdev = dev->media_dev;
-#endif
+	dvb_register_media_controller(&dvb->adapter, dev->media_dev);
 
 	/* Ensure all frontends negotiate bus access */
 	dvb->frontend->ops.ts_bus_ctrl = cx231xx_dvb_bus_ctrl;

drivers/media/usb/dvb-usb-v2/dvb_usb_core.c

···
 		return;
 	}
 
-	adap->dvb_adap.mdev = mdev;
+	dvb_register_media_controller(&adap->dvb_adap, mdev);
 
 	dev_info(&d->udev->dev, "media controller created\n");
 

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

···
 		kfree(mdev);
 		return;
 	}
-	adap->dvb_adap.mdev = mdev;
+	dvb_register_media_controller(&adap->dvb_adap, mdev);
 
 	dev_info(&d->udev->dev, "media controller created\n");
 #endif