usb: gadget: Fix return value check in r8a66597_probe()

In case of error, the function devm_ioremap_resource() returns ERR_PTR()
and never returns NULL. The NULL test in the return value check should
be replaced with IS_ERR().
Acked-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/udc/r8a66597-udc.c

@@ -1868,8 +1868,8 @@ static int r8a66597_probe(struct platform_device *pdev)
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	reg = devm_ioremap_resource(&pdev->dev, res);
-	if (!reg)
-		return -ENODEV;
+	if (IS_ERR(reg))
+		return PTR_ERR(reg);
 
 	ires = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
 	irq = ires->start;