leds: trigger: gpio: Avoid warning on update of inverted

If the GPIO has not been configured yet, writing to inverted will raise
a kernel warning.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

drivers/leds/trigger/ledtrig-gpio.c

@@ -99,6 +99,7 @@ static ssize_t gpio_trig_inverted_store(struct device *dev,
 	gpio_data->inverted = inverted;
 
 	/* After inverting, we need to update the LED. */
+	if (gpio_is_valid(gpio_data->gpio))
 		gpio_trig_irq(0, led);
 
 	return n;