USB: mos7840: fix urb leak at release

Make sure control urb is freed at release.

Cc: <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/mos7840.c

@@ -2645,6 +2645,7 @@ static void mos7840_release(struct usb_serial *serial)
 				del_timer_sync(&mos7840_port->led_timer1);
 				del_timer_sync(&mos7840_port->led_timer2);
 			}
+			usb_free_urb(mos7840_port->control_urb);
 			kfree(mos7840_port->ctrl_buf);
 			kfree(mos7840_port->dr);
 			kfree(mos7840_port);