net: enetc: fix an issue about leak system resources

the related system resources were not released when enetc_hw_alloc()
return error in the enetc_pci_mdio_probe(), add iounmap() for error
handling label "err_hw_alloc" to fix it.

Fixes: 6517798 ("enetc: Make MDIO accessors more generic and export to include/linux/fsl")
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Dejin Zheng <zhengdejin5@gmail.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/enetc/enetc_pci_mdio.c

@@ -74,8 +74,8 @@ static int enetc_pci_mdio_probe(struct pci_dev *pdev,
 	pci_disable_device(pdev);
 err_pci_enable:
 err_mdiobus_alloc:
-	iounmap(port_regs);
 err_hw_alloc:
+	iounmap(port_regs);
 err_ioremap:
 	return err;
 }