net/fsl: xgmac_mdio: fix return value check in xgmac_mdio_probe()

In case of error, the function devm_ioremap() returns NULL pointer
not ERR_PTR(). The IS_ERR() test in the return value check should
be replaced with NULL test.

Fixes: 1d14eb15dc2c ("net/fsl: xgmac_mdio: Use managed device resources")
Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Wei Yongjun <[e-mail]>
Reviewed-by: Tobias Waldekranz <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/freescale/xgmac_mdio.c

···
 	priv = bus->priv;
 	priv->mdio_base = devm_ioremap(&pdev->dev, res->start,
 				       resource_size(res));
-	if (IS_ERR(priv->mdio_base))
-		return PTR_ERR(priv->mdio_base);
+	if (!priv->mdio_base)
+		return -ENOMEM;
 
 	/* For both ACPI and DT cases, endianness of MDIO controller
 	 * needs to be specified using "little-endian" property.