gpiolib: Fix GPIO chip IRQ initialization restriction

In case of gpio-regmap, IRQ chip is added by regmap-irq and associated with
GPIO chip by gpiochip_irqchip_add_domain(). The initialization flag was not
added in gpiochip_irqchip_add_domain(), causing gpiochip_to_irq() to return
-EPROBE_DEFER.

Fixes: 5467801 ("gpio: Restrict usage of GPIO chip irq members before initialization")
Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Author: Jiawen Wu

drivers/gpio/gpiolib.c

@@ -1792,6 +1792,14 @@ int gpiochip_irqchip_add_domain(struct gpio_chip *gc,
 	gc->to_irq = gpiochip_to_irq;
 	gc->irq.domain = domain;
 
+	/*
+	 * Using barrier() here to prevent compiler from reordering
+	 * gc->irq.initialized before adding irqdomain.
+	 */
+	barrier();
+
+	gc->irq.initialized = true;
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(gpiochip_irqchip_add_domain);