lan743x: fix use of uninitialized variable

When no devicetree is present, the driver will use an
uninitialized variable.

Fix by initializing this variable.

Fixes: 902a66e ("lan743x: correctly handle chips with internal PHY")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com>
Link: https://lore.kernel.org/r/20201112152513.1941-1-TheSven73@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/microchip/lan743x_main.c

@@ -1014,8 +1014,8 @@ static void lan743x_phy_close(struct lan743x_adapter *adapter)
 static int lan743x_phy_open(struct lan743x_adapter *adapter)
 {
 	struct lan743x_phy *phy = &adapter->phy;
+	struct phy_device *phydev = NULL;
 	struct device_node *phynode;
-	struct phy_device *phydev;
 	struct net_device *netdev;
 	int ret = -EIO;