gpio: don't override irq_*_resources() callbacks

If the driver has specified its own irq_{request/release}_resources()
functions, don't override them.  The gpio-etraxfs driver will use this.
Signed-off-by: Rabin Vincent <rabin@rab.in>
[Added a small comment blurb]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -641,8 +641,16 @@ int gpiochip_irqchip_add(struct gpio_chip *gpiochip,
 		gpiochip->irqchip = NULL;
 		return -EINVAL;
 	}
-	irqchip->irq_request_resources = gpiochip_irq_reqres;
-	irqchip->irq_release_resources = gpiochip_irq_relres;
+
+	/*
+	 * It is possible for a driver to override this, but only if the
+	 * alternative functions are both implemented.
+	 */
+	if (!irqchip->irq_request_resources &&
+	    !irqchip->irq_release_resources) {
+		irqchip->irq_request_resources = gpiochip_irq_reqres;
+		irqchip->irq_release_resources = gpiochip_irq_relres;
+	}
 
 	/*
 	 * Prepare the mapping since the irqchip shall be orthogonal to