Bluetooth: hci_ldisc: Provide a 'default' switch case

When both CONFIG_BT_HCIUART_INTEL and CONFIG_BT_HCIUART_BCM are not
selected, sparse complains like this:

drivers/bluetooth/hci_ldisc.c:437:9: warning: switch with no cases

Fix the sparse warning by proving a default switch case.
Signed-off-by: NFabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/hci_ldisc.c

@@ -447,6 +447,8 @@ static int hci_uart_setup(struct hci_dev *hdev)
 		btbcm_check_bdaddr(hdev);
 		break;
 #endif
+	default:
+		break;
 	}
 
 done: