gpio: mpc8xxx: Fix IRQ check in mpc8xxx_probe

platform_get_irq() returns negative error number instead 0 on failure.
And the doc of platform_get_irq() provides a usage example:

    int irq = platform_get_irq(pdev, 0);
    if (irq < 0)
        return irq;

Fix the check of return value to catch errors correctly.

Fixes: 76c47d14 ("gpio: mpc8xxx: Add ACPI support")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

drivers/gpio/gpio-mpc8xxx.c

@@ -388,8 +388,8 @@ static int mpc8xxx_probe(struct platform_device *pdev)
 	}
 
 	mpc8xxx_gc->irqn = platform_get_irq(pdev, 0);
-	if (!mpc8xxx_gc->irqn)
-		return 0;
+	if (mpc8xxx_gc->irqn < 0)
+		return mpc8xxx_gc->irqn;
 
 	mpc8xxx_gc->irq = irq_domain_create_linear(fwnode,
 						   MPC8XXX_GPIO_PINS,