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=e330b9a6bb35dc7097a4f02cb1ae7b6f96df92af

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>

drivers/gpio/gpio-msic.c

@@ -265,8 +265,8 @@ static int platform_msic_gpio_probe(struct platform_device *pdev)
 	int i;
 
 	if (irq < 0) {
-		dev_err(dev, "no IRQ line\n");
-		return -EINVAL;
+		dev_err(dev, "no IRQ line: %d\n", irq);
+		return irq;
 	}
 
 	if (!pdata || !pdata->gpio_base) {