gpiolib: Drop unused domain_ops memeber of GPIO IRQ chip

It seems there is no driver that requires custom IRQ chip
domain options. Drop the member and respective code.

Signed-off-by: Andy Shevchenko <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Acked-by: Marc Zyngier <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpiolib.c

···
 		if (ret)
 			return ret;
 	} else {
-		/* Some drivers provide custom irqdomain ops */
 		gc->irq.domain = irq_domain_create_simple(fwnode,
 			gc->ngpio,
 			gc->irq.first,
-			gc->irq.domain_ops ?: &gpiochip_domain_ops,
+			&gpiochip_domain_ops,
 			gc);
 		if (!gc->irq.domain)
 			return -EINVAL;

include/linux/gpio/driver.h

···
 	 */
 	struct irq_domain *domain;
 
-	/**
-	 * @domain_ops:
-	 *
-	 * Table of interrupt domain operations for this IRQ chip.
-	 */
-	const struct irq_domain_ops *domain_ops;
-
 #ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
 	/**
 	 * @fwnode: