[media] drivers/media/media-device: fix double free bug in _unregister()

While removing all interfaces in media_device_unregister(), all
media_interface pointers are freed.  This is illegal and results in
double kfree() if any media_interface is still linked at this point;
maybe because a userspace process still has a file handle.  Once the
process closes the file handle, dvb_media_device_free() gets called,
which frees the dvb_device.intf_devnode again.

This patch removes the unnecessary kfree() call, and documents who's
responsible for really freeing it.
Signed-off-by: Max Kellermann <max.kellermann@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/media-device.c

@@ -801,9 +801,13 @@ void media_device_unregister(struct media_device *mdev)
 	/* Remove all interfaces from the media device */
 	list_for_each_entry_safe(intf, tmp_intf, &mdev->interfaces,
 				 graph_obj.list) {
+		/*
+		 * Unlink the interface, but don't free it here; the
+		 * module which created it is responsible for freeing
+		 * it
+		 */
 		__media_remove_intf_links(intf);
 		media_gobj_destroy(&intf->graph_obj);
-		kfree(intf);
 	}
 
 	mutex_unlock(&mdev->graph_mutex);