smsc75xx: fix mdio reads and writes

smsc75xx needs MII_ACCESS_BUSY to be set to correctly trigger mdio I/O.  Note smsc75xx is different from smsc95xx in this regard.
Signed-off-by: Stephane Fillod <fillods@users.sf.net>
Signed-off-by: Steve Glendinning <steve.glendinning@shawell.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/smsc75xx.c

@@ -171,7 +171,7 @@ static int smsc75xx_mdio_read(struct net_device *netdev, int phy_id, int idx)
 	idx &= dev->mii.reg_num_mask;
 	addr = ((phy_id << MII_ACCESS_PHY_ADDR_SHIFT) & MII_ACCESS_PHY_ADDR)
 		| ((idx << MII_ACCESS_REG_ADDR_SHIFT) & MII_ACCESS_REG_ADDR)
-		| MII_ACCESS_READ;
+		| MII_ACCESS_READ | MII_ACCESS_BUSY;
 	ret = smsc75xx_write_reg(dev, MII_ACCESS, addr);
 	check_warn_goto_done(ret, "Error writing MII_ACCESS");
 
@@ -210,7 +210,7 @@ static void smsc75xx_mdio_write(struct net_device *netdev, int phy_id, int idx,
 	idx &= dev->mii.reg_num_mask;
 	addr = ((phy_id << MII_ACCESS_PHY_ADDR_SHIFT) & MII_ACCESS_PHY_ADDR)
 		| ((idx << MII_ACCESS_REG_ADDR_SHIFT) & MII_ACCESS_REG_ADDR)
-		| MII_ACCESS_WRITE;
+		| MII_ACCESS_WRITE | MII_ACCESS_BUSY;
 	ret = smsc75xx_write_reg(dev, MII_ACCESS, addr);
 	check_warn_goto_done(ret, "Error writing MII_ACCESS");