staging: octeon-ethernet: support of_get_mac_address new ERR_PTR error

There was NVMEM support added to of_get_mac_address, so it could now return
ERR_PTR encoded error values, so we need to adjust all current users of
of_get_mac_address to this new fact.
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/staging/octeon/ethernet.c

@@ -421,7 +421,7 @@ int cvm_oct_common_init(struct net_device *dev)
 	if (priv->of_node)
 		mac = of_get_mac_address(priv->of_node);
 
-	if (mac)
+	if (!IS_ERR(mac))
 		ether_addr_copy(dev->dev_addr, mac);
 	else
 		eth_hw_addr_random(dev);