gpio: mpc8xxx: Fix IRQ check in mpc8xxx_probe

gpio: mpc8xxx: Fix IRQ check in mpc8xxx_probe

commit 0b39536cc699db6850c426db7f9cb45923de40c5 upstream.

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: 76c47d1449fc ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>