Bluetooth: add NULL pointer check in HCI

If we fail to find a hci device pointer in hci_uart, don't try
to deref the NULL one we do have.
Signed-off-by: Jun Nie <njun@marvell.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

drivers/bluetooth/hci_ldisc.c

@@ -311,10 +311,12 @@ static void hci_uart_tty_close(struct tty_struct *tty)
 
 		if (test_and_clear_bit(HCI_UART_PROTO_SET, &hu->flags)) {
 			hu->proto->close(hu);
+			if (hdev) {
 				hci_unregister_dev(hdev);
 				hci_free_dev(hdev);
 			}
 		}
+	}
 }
 
 /* hci_uart_tty_wakeup()