RGB led driver: More retries on boot

src/drivers/rgbled/rgbled.cpp

@@ -181,12 +181,18 @@ RGBLED::probe()
 	   to be enough, as the 3rd one consistently fails if no
 	   RGBLED is on the bus.
 	 */
+
+	unsigned prevretries = _retries;
+	_retries = 4;
+
 	if ((ret=get(on, powersave, r, g, b)) != OK ||
 	    (ret=send_led_enable(false) != OK) ||
 	    (ret=send_led_enable(false) != OK)) {
 		return ret;
 	}
 
+	_retries = prevretries;
+
 	return ret;
 }