net/mlxbf_gige: Fix an IS_ERR() vs NULL bug in mlxbf_gige_mdio_probe

The devm_ioremap() function returns NULL on error, it doesn't return
error pointers.

Fixes: 3a1a274e ("mlxbf_gige: compute MDIO period based on i1clk")
Signed-off-by: Peng Wu <wupeng58@huawei.com>
Link: https://lore.kernel.org/r/20220923023640.116057-1-wupeng58@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mellanox/mlxbf_gige/mlxbf_gige_mdio.c

@@ -246,8 +246,8 @@ int mlxbf_gige_mdio_probe(struct platform_device *pdev, struct mlxbf_gige *priv)
 	}
 
 	priv->clk_io = devm_ioremap(dev, res->start, resource_size(res));
-	if (IS_ERR(priv->clk_io))
-		return PTR_ERR(priv->clk_io);
+	if (!priv->clk_io)
+		return -ENOMEM;
 
 	mlxbf_gige_mdio_cfg(priv);