gpio: mockup: fix a potential crash when creating debugfs entries

If we failed to create the top debugfs directory, we must not try to
create the child nodes. We currently only check if gpio_mockup_dbg_dir
is not NULL, but it can also contain an errno if debugfs is disabled
in build options. Use IS_ERR_OR_NULL() instead.
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-mockup.c

@@ -314,7 +314,7 @@ static int gpio_mockup_probe(struct platform_device *pdev)
 	if (rv)
 		return rv;
 
-	if (gpio_mockup_dbg_dir)
+	if (!IS_ERR_OR_NULL(gpio_mockup_dbg_dir))
 		gpio_mockup_debugfs_setup(dev, chip);
 
 	return 0;