[IRDA]: mcs7780 needs to free allocated rx buffer.

While testing the mcs7780 based IrDA USB dongle I've stumbled upon
memory leak in mcs_net_close(). Patch below fixes it.
Signed-off-by: Hinko Kocevar <hinko.kocevar@cetrtapot.si>
Signed-off-by: Samuel Ortiz <samuel@sortiz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/irda/mcs7780.c

@@ -677,6 +677,8 @@ static int mcs_net_close(struct net_device *netdev)
 	/* Stop transmit processing */
 	netif_stop_queue(netdev);
 
+	kfree_skb(mcs->rx_buff.skb);
+
 	/* kill and free the receive and transmit URBs */
 	usb_kill_urb(mcs->rx_urb);
 	usb_free_urb(mcs->rx_urb);