pinctrl: nuvoton: npcm7xx: constify copied structure

The npcmgpio_irqchip structure is only copied into another
structure, so make it const.

The opportunity for this change was found using Coccinelle.
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

Link: https://lore.kernel.org/r/1577864614-5543-17-git-send-email-Julia.Lawall@inria.frSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/nuvoton/pinctrl-npcm7xx.c

@@ -331,7 +331,7 @@ static unsigned int npcmgpio_irq_startup(struct irq_data *d)
 	return 0;
 }
 
-static struct irq_chip npcmgpio_irqchip = {
+static const struct irq_chip npcmgpio_irqchip = {
 	.name = "NPCM7XX-GPIO-IRQ",
 	.irq_ack = npcmgpio_irq_ack,
 	.irq_unmask = npcmgpio_irq_unmask,