Staging: most: fix double unlock

This patch fixes double unlocking of a spinlock the aim-v4l2 module.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Andrey Shvetsov <andrey.shvetsov@k2l.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/most/aim-v4l2/video.c

@@ -619,6 +619,7 @@ static void __exit aim_exit(void)
 		aim_unregister_videodev(mdev);
 		v4l2_device_disconnect(&mdev->v4l2_dev);
 		v4l2_device_put(&mdev->v4l2_dev);
+		spin_lock(&list_lock);
 	}
 	spin_unlock(&list_lock);