net/fsl: fix a bug in xgmac_mdio

There is a bug in xgmac_mdio_read when clear the bit MDIO_STAT_ENC,
which '&' is missed in 'mdio_stat &= ~MDIO_STAT_ENC'.
Signed-off-by: NShaohui Xie <Shaohui.Xie@freescale.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/xgmac_mdio.c

@@ -156,7 +156,7 @@ static int xgmac_mdio_read(struct mii_bus *bus, int phy_id, int regnum)
 		mdio_stat |= MDIO_STAT_ENC;
 	} else {
 		dev_addr = regnum & 0x1f;
-		mdio_stat = ~MDIO_STAT_ENC;
+		mdio_stat &= ~MDIO_STAT_ENC;
 	}
 
 	out_be32(&regs->mdio_stat, mdio_stat);