gpio: msic: fix error return code in platform_msic_gpio_probe()

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

Notice that platform_get_irq() no longer returns 0 on error:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e330b9a6



Print and propagate the return value of platform_get_irq on failure.

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