net: xgene: fix maybe-uninitialized variable

Building with -Wmaybe-uninitialized shows a potential use of
an uninitialized variable:

drivers/net/ethernet/apm/xgene/xgene_enet_hw.c: In function 'xgene_enet_phy_connect':
drivers/net/ethernet/apm/xgene/xgene_enet_hw.c:802:23: warning: 'phy_dev' may be used uninitialized in this function [-Wmaybe-uninitialized]

Although the compiler correctly identified this based on the function,
the current code is still safe as long dev->of_node is non-NULL
for the case of CONFIG_ACPI=n, which is currently the case.

The warning is now disabled by default, but still appears when
building with W=1, and other build test tools should be able to
detect it as well. Adding an #else clause here makes the code
more robust and makes it clear to the compiler that this cannot
happen.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 8089a96f601b ("drivers: net: xgene: Add backward compatibility")
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/apm/xgene/xgene_enet_hw.c

@@ -793,6 +793,8 @@ int xgene_enet_phy_connect(struct net_device *ndev)
 			netdev_err(ndev, "Could not connect to PHY\n");
 			return  -ENODEV;
 		}
+#else
+		return -ENODEV;
 #endif
 	}