gpio: raspberrypi-exp: decrease refcount on firmware dt node

We're getting a reference RPi's firmware node in order to be able to
communicate with it's driver. We should decrease the reference count on
the dt node after being done with it.

Fixes: a98d90e7d5 ("gpio: raspberrypi-exp: Driver for RPi3 GPIO expander via mailbox service")
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-raspberrypi-exp.c

@@ -206,6 +206,7 @@ static int rpi_exp_gpio_probe(struct platform_device *pdev)
 	}
 
 	fw = rpi_firmware_get(fw_node);
+	of_node_put(fw_node);
 	if (!fw)
 		return -EPROBE_DEFER;