gpio: raspberrypi-exp: Release firmware handle on unbind

Use devm_rpi_firmware_get() so as to make sure we release RPi's firmware
interface when unbinding the device.
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpio-raspberrypi-exp.c

@@ -208,7 +208,7 @@ static int rpi_exp_gpio_probe(struct platform_device *pdev)
 		return -ENOENT;
 	}
 
-	fw = rpi_firmware_get(fw_node);
+	fw = devm_rpi_firmware_get(&pdev->dev, fw_node);
 	of_node_put(fw_node);
 	if (!fw)
 		return -EPROBE_DEFER;