Add a dummy implementation to make bt_disable() not fail

To allow turning Bluetooth on and off on the Track Mini.

Author: sense-Jo

drivers/bluetooth/hci/h4.c

@@ -527,10 +527,18 @@ static int h4_setup(const struct bt_hci_setup_params *params)
 }
 #endif
 
+static int h4_close(void)
+{
+	/* NOTE: dummy implementition to make bt_disable not fail – ESP32 is
+	 * turned off after that anyways */
+	return 0;
+}
+
 static const struct bt_hci_driver drv = {
 	.name		= "H:4",
 	.bus		= BT_HCI_DRIVER_BUS_UART,
 	.open		= h4_open,
+	.close		= h4_close,
 	.send		= h4_send,
 #if defined(CONFIG_BT_HCI_SETUP)
 	.setup		= h4_setup