gpio: idt3243x: Fix return value check in idt_gpio_probe()

In case of error, the function devm_platform_ioremap_resource_byname()
returns ERR_PTR() and never returns NULL. The NULL test in the return
value check should be replaced with IS_ERR().

Fixes: 4195926aedca ("gpio: Add support for IDT 79RC3243x GPIO controller")
Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Wei Yongjun <[e-mail]>
Acked-by: Linus Walleij <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpio-idt3243x.c

···
 		return -ENOMEM;
 
 	ctrl->gpio = devm_platform_ioremap_resource_byname(pdev, "gpio");
-	if (!ctrl->gpio)
-		return -ENOMEM;
+	if (IS_ERR(ctrl->gpio))
+		return PTR_ERR(ctrl->gpio);
 
 	ctrl->gc.parent = dev;
 
···
 
 	if (device_property_read_bool(dev, "interrupt-controller")) {
 		ctrl->pic = devm_platform_ioremap_resource_byname(pdev, "pic");
-		if (!ctrl->pic)
-			return -ENOMEM;
+		if (IS_ERR(ctrl->pic))
+			return PTR_ERR(ctrl->pic);
 
 		parent_irq = platform_get_irq(pdev, 0);
 		if (!parent_irq)