net: zynq: Use predefined macros instead of hardcoded value

MII is used by this driver.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

drivers/net/zynq_gem.c

@@ -338,7 +338,8 @@ static int zynq_gem_init(struct eth_device *dev, bd_t * bis)
 	phy_detection(dev);
 
 	/* interface - look at tsec */
-	phydev = phy_connect(priv->bus, priv->phyaddr, dev, 0);
+	phydev = phy_connect(priv->bus, priv->phyaddr, dev,
+			     PHY_INTERFACE_MODE_MII);
 
 	phydev->supported = supported | ADVERTISED_Pause |
 			    ADVERTISED_Asym_Pause;