USB: serial: metro-usb: stop I/O after failed open

Make sure to kill the interrupt-in URB after a failed open request.
Apart from saving power (and avoiding stale input after a later
successful open), this also prevents a NULL-deref in the completion
handler if the port is manually unbound.
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Fixes: 70457786 ("USB: serial: metro-usb: get data from device in Uni-Directional mode.")
Cc: stable <stable@vger.kernel.org>	# 3.5
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/metro-usb.c

@@ -188,7 +188,7 @@ static int metrousb_open(struct tty_struct *tty, struct usb_serial_port *port)
 		dev_err(&port->dev,
 			"%s - failed submitting interrupt in urb, error code=%d\n",
 			__func__, result);
-		goto exit;
+		return result;
 	}
 
 	/* Send activate cmd to device */
@@ -197,9 +197,14 @@ static int metrousb_open(struct tty_struct *tty, struct usb_serial_port *port)
 		dev_err(&port->dev,
 			"%s - failed to configure device, error code=%d\n",
 			__func__, result);
-		goto exit;
+		goto err_kill_urb;
 	}
-exit:
+
+	return 0;
+
+err_kill_urb:
+	usb_kill_urb(port->interrupt_in_urb);
+
 	return result;
 }