gpio: gpio-reg: fix build

Revert changes introduced by commit f0fbe7b ("gpio: Move irqdomain
into struct gpio_irq_chip") as they are not aplicable to this driver.

Reported-by: Russell King - ARM Linux <linux@armlinux.org.uk>
Fixes: f0fbe7b ("gpio: Move irqdomain into struct gpio_irq_chip")
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-reg.c

@@ -103,8 +103,8 @@ static int gpio_reg_to_irq(struct gpio_chip *gc, unsigned offset)
 	struct gpio_reg *r = to_gpio_reg(gc);
 	int irq = r->irqs[offset];
 
-	if (irq >= 0 && r->irq.domain)
-		irq = irq_find_mapping(r->irq.domain, irq);
+	if (irq >= 0 && r->irqdomain)
+		irq = irq_find_mapping(r->irqdomain, irq);
 
 	return irq;
 }