thermostat: fix comment for gcc

soft/thermostat/src/mainwindow.cpp

@@ -415,9 +415,9 @@ void MainWindow::apply_order_to_heaters(void)
 		break;
 	case ON:
 		heating_order = true;
-		/* fall */
+		/* fall through */
 	case OFF:
-		/* fall */
+		/* fall through */
 	default:
 		emit setAllHeatersOn(heating_order);