V4L/DVB: drivers/media/radio/si470x/radio-si470x-usb.c fix use after free

In si470x_usb_driver_disconnect() radio->disconnect_lock is accessed
after it is freed. This fixes the problem.

Coverity CID: 2530
Signed-off-by: Darren Jenkins <darrenrjenkins@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/radio/si470x/radio-si470x-usb.c

@@ -842,9 +842,11 @@ static void si470x_usb_driver_disconnect(struct usb_interface *intf)
 		kfree(radio->int_in_buffer);
 		video_unregister_device(radio->videodev);
 		kfree(radio->buffer);
+		mutex_unlock(&radio->disconnect_lock);
 		kfree(radio);
+	} else {
+		mutex_unlock(&radio->disconnect_lock);
 	}
-	mutex_unlock(&radio->disconnect_lock);
 }