net: thunderx: avoid null pointer dereference

In function bgx_lmac_handler only use a member of
lmac after checking it is not null.
Signed-off-by: NHeinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: NDavid Daney <david.daney@cavium.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/cavium/thunder/thunder_bgx.c

@@ -274,12 +274,14 @@ static void bgx_sgmii_change_link_state(struct lmac *lmac)
 static void bgx_lmac_handler(struct net_device *netdev)
 {
 	struct lmac *lmac = container_of(netdev, struct lmac, netdev);
-	struct phy_device *phydev = lmac->phydev;
+	struct phy_device *phydev;
 	int link_changed = 0;
 
 	if (!lmac)
 		return;
 
+	phydev = lmac->phydev;
+
 	if (!phydev->link && lmac->last_link)
 		link_changed = -1;