gpio: madera: Add missing const

madera_gpio_chip is only used as a template so it can be marked as const.
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpio-madera.c

@@ -107,7 +107,7 @@ static void madera_gpio_set(struct gpio_chip *chip, unsigned int offset,
 			 MADERA_GPIO1_CTRL_1 + reg_offset, ret);
 }
 
-static struct gpio_chip madera_gpio_chip = {
+static const struct gpio_chip madera_gpio_chip = {
 	.label			= "madera",
 	.owner			= THIS_MODULE,
 	.request		= gpiochip_generic_request,