gpio: constify of_phandle_args in of_find_gpio_device_by_xlate()

Pointer to the struct of_phandle_args can be made const after
gpio_device_find() arguments got constified.  This should be part of
commit 4a92857d ("gpio: constify opaque pointer "data" in
gpio_device_find()").
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

drivers/gpio/gpiolib-of.c

@@ -129,7 +129,7 @@ static int of_gpiochip_match_node_and_xlate(struct gpio_chip *chip,
 }
 
 static struct gpio_device *
-of_find_gpio_device_by_xlate(struct of_phandle_args *gpiospec)
+of_find_gpio_device_by_xlate(const struct of_phandle_args *gpiospec)
 {
 	return gpio_device_find(gpiospec, of_gpiochip_match_node_and_xlate);
 }