[media] media: add messages when media device gets (un)registered

We can only free the media device after being sure that no
graph object is used.

In order to help tracking it, let's add debug messages
that will print when the media controller gets registered
or unregistered.
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/media-device.c

@@ -359,6 +359,7 @@ static DEVICE_ATTR(model, S_IRUGO, show_model, NULL);
 
 static void media_device_release(struct media_devnode *mdev)
 {
+	dev_dbg(mdev->parent, "Media device released\n");
 }
 
 /**
@@ -397,6 +398,8 @@ int __must_check __media_device_register(struct media_device *mdev,
 		return ret;
 	}
 
+	dev_dbg(mdev->dev, "Media device registered\n");
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(__media_device_register);
@@ -416,6 +419,8 @@ void media_device_unregister(struct media_device *mdev)
 
 	device_remove_file(&mdev->devnode.dev, &dev_attr_model);
 	media_devnode_unregister(&mdev->devnode);
+
+	dev_dbg(mdev->dev, "Media device unregistered\n");
 }
 EXPORT_SYMBOL_GPL(media_device_unregister);