net: bcm63xx: avoid referencing uninitialized variable

gcc found a reference to an uninitialized variable in the error handling
of bcm_enet_open, introduced by a recent cleanup:

drivers/net/ethernet/broadcom/bcm63xx_enet.c: In function 'bcm_enet_open'
drivers/net/ethernet/broadcom/bcm63xx_enet.c:1129:2: warning: 'phydev' may be used uninitialized in this function [-Wmaybe-uninitialized]

This makes the use of that variable conditional, so we only reference it
here after it has been used before. Unlike my normal patches, I have not
build-tested this one, as I don't currently have mips test in my
randconfig setup.

Fixes: 625eb866 ("net: ethernet: broadcom: bcm63xx: use phydev from struct net_device")
Cc: Philippe Reynes <tremyfr@gmail.com>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bcm63xx_enet.c

@@ -1126,7 +1126,8 @@ static int bcm_enet_open(struct net_device *dev)
 	free_irq(dev->irq, dev);
 
 out_phy_disconnect:
-	phy_disconnect(phydev);
+	if (priv->has_phy)
+		phy_disconnect(phydev);
 
 	return ret;
 }