Fix int overflow

Firmware/ultralcd.cpp

@@ -7041,7 +7041,7 @@ static bool lcd_selftest_fan_dialog(int _fan)
 static int lcd_selftest_screen(int _step, int _progress, int _progress_scale, bool _clear, int _delay)
 {
 
-	lcd_next_update_millis = millis() + (LCD_UPDATE_INTERVAL * 10000);
+	lcd_next_update_millis = millis() + (LCD_UPDATE_INTERVAL * 10000L);
 
 	int _step_block = 0;
 	const char *_indicator = (_progress > _progress_scale) ? "-" : "|";