net: lantiq: Fix return value check in xrx200_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().

Fixes: fe1a56420cf2 ("net: lantiq: Add Lantiq / Intel VRX200 Ethernet driver")
Signed-off-by: Wei Yongjun <[e-mail]>
Acked-by: Hauke Mehrtens <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/lantiq_xrx200.c

···
 	}
 
 	priv->pmac_reg = devm_ioremap_resource(dev, res);
-	if (!priv->pmac_reg) {
+	if (IS_ERR(priv->pmac_reg)) {
 		dev_err(dev, "failed to request and remap io ranges\n");
-		return -ENOMEM;
+		return PTR_ERR(priv->pmac_reg);
 	}
 
 	priv->chan_rx.dma.irq = platform_get_irq_byname(pdev, "rx");