ixgbe: Return error when getting PHY address if PHY access is not supported

In cases where PHY register access is not supported, don't mislead
a caller into thinking that it is supported by returning a PHY
address. Instead, return -EOPNOTSUPP when PHY access is not
supported.
Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -8529,6 +8529,10 @@ static int ixgbe_ioctl(struct net_device *netdev, struct ifreq *req, int cmd)
 		return ixgbe_ptp_set_ts_config(adapter, req);
 	case SIOCGHWTSTAMP:
 		return ixgbe_ptp_get_ts_config(adapter, req);
+	case SIOCGMIIPHY:
+		if (!adapter->hw.phy.ops.read_reg)
+			return -EOPNOTSUPP;
+		/* fall through */
 	default:
 		return mdio_mii_ioctl(&adapter->hw.phy.mdio, if_mii(req), cmd);
 	}