net: stmmac: Fix error path after register_netdev move

commit b2eb09af upstream.

Commit 57016590 ("net: stmmac: Fix race between stmmac_drv_probe and
stmmac_open") re-ordered how the MDIO bus registration and the network
device are registered, but missed to unwind the MDIO bus registration in
case we fail to register the network device.

Fixes: 57016590 ("net: stmmac: Fix race between stmmac_drv_probe and stmmac_open")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Kweh, Hock Leong <hock.leong.kweh@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16:
 - stmmac_dvr_probe() returns a pointer
 - 'pcs' is a member of struct stmmac_priv, not struct mac_device_info]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -2794,12 +2794,19 @@ struct stmmac_priv *stmmac_dvr_probe(struct device *device,
 	}
 
 	ret = register_netdev(ndev);
-	if (ret)
+	if (ret) {
 		netdev_err(priv->dev, "%s: ERROR %i registering the device\n",
 			   __func__, ret);
+		goto error_netdev_register;
+	}
 
-	return ret ? ERR_PTR(ret) : priv;
+	return priv;
 
+error_netdev_register:
+	if (priv->pcs != STMMAC_PCS_RGMII &&
+	    priv->pcs != STMMAC_PCS_TBI &&
+	    priv->pcs != STMMAC_PCS_RTBI)
+		stmmac_mdio_unregister(ndev);
 error_mdio_register:
 	netif_napi_del(&priv->napi);
 error_hw_init: