bcm63xx_enet: avoid uninitialized variable warning

gcc-7 and probably earlier versions get confused by this function
and print a harmless warning:

drivers/net/ethernet/broadcom/bcm63xx_enet.c: In function 'bcm_enet_open':
drivers/net/ethernet/broadcom/bcm63xx_enet.c:1130:3: error: 'phydev' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This adds an initialization for the 'phydev' variable when it is unused
and changes the check to test for that NULL pointer to make it clear
that we always pass a valid pointer here.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bcm63xx_enet.c

@@ -913,6 +913,8 @@ static int bcm_enet_open(struct net_device *dev)
 		priv->old_link = 0;
 		priv->old_duplex = -1;
 		priv->old_pause = -1;
+	} else {
+		phydev = NULL;
 	}
 
 	/* mask all interrupts and request them */
@@ -1083,7 +1085,7 @@ static int bcm_enet_open(struct net_device *dev)
 	enet_dmac_writel(priv, priv->dma_chan_int_mask,
 			 ENETDMAC_IRMASK, priv->tx_chan);
 
-	if (priv->has_phy)
+	if (phydev)
 		phy_start(phydev);
 	else
 		bcm_enet_adjust_link(dev);
@@ -1126,7 +1128,7 @@ static int bcm_enet_open(struct net_device *dev)
 	free_irq(dev->irq, dev);
 
 out_phy_disconnect:
-	if (priv->has_phy)
+	if (phydev)
 		phy_disconnect(phydev);
 
 	return ret;