bcm63xx_enet: fix return value check in bcm_enet_shared_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().

Introduce by commit 0ae99b5fede6f3a8d252d50bb4aba29544295219
(bcm63xx_enet: split DMA channel register accesses)

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bcm63xx_enet.c

@@ -2862,8 +2862,8 @@ static int bcm_enet_shared_probe(struct platform_device *pdev)
 	for (i = 0; i < 3; i++) {
 		res = platform_get_resource(pdev, IORESOURCE_MEM, i);
 		p[i] = devm_ioremap_resource(&pdev->dev, res);
-		if (!p[i])
-			return -ENOMEM;
+		if (IS_ERR(p[i]))
+			return PTR_ERR(p[i]);
 	}
 
 	memcpy(bcm_enet_shared_base, p, sizeof(bcm_enet_shared_base));