gpio: mockup: don't return magic numbers from probe()

When the requested number of GPIO lines is 0, return -EINVAL, not
-1 which is -EPERM.

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-mockup.c

@@ -369,7 +369,7 @@ static int gpio_mockup_probe(struct platform_device *pdev)
 			ret = gpio_mockup_add(dev, &chips[i],
 					      chip_name, base, ngpio);
 		} else {
-			ret = -1;
+			ret = -EINVAL;
 		}
 
 		if (ret) {