pinctrl: amd: fix error return code in amd_gpio_probe()

platform_get_irq() returns an error code, but the pinctrl-amd driver
ignores it and always returns -EINVAL. This is not correct and,
prevents -EPROBE_DEFER from being propagated properly.

Print and propagate the return value of platform_get_irq on failure.

This issue was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>