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 <[e-mail]>
Signed-off-by: Pavel Machek <[e-mail]>

drivers/leds/trigger/ledtrig-gpio.c

···
 	gpio_data->inverted = inverted;
 
 	/* After inverting, we need to update the LED. */
-	gpio_trig_irq(0, led);
+	if (gpio_is_valid(gpio_data->gpio))
+		gpio_trig_irq(0, led);
 
 	return n;
 }