net: xgene: avoid bogus maybe-uninitialized warning

In some configurations, gcc cannot trace the state of variables
across a spin_unlock() barrier, leading to a warning about
correct code:

xgene_enet_main.c: In function 'xgene_enet_start_xmit':
../../../phy/mdio-xgene.h:112:14: error: 'mss_index' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Here we can trivially move the assignment before that spin_unlock,
which reliably avoids the warning.

Fixes: e3978673f5 ("drivers: net: xgene: Fix MSS programming")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -319,11 +319,11 @@ static int xgene_enet_setup_mss(struct net_device *ndev, u32 mss)
 		}
 	}
 
-	spin_unlock(&pdata->mss_lock);
-
 	/* No slots with ref_count = 0 available, return busy */
 	if (!mss_index_found)
-		return -EBUSY;
+		mss_index = -EBUSY;
+
+	spin_unlock(&pdata->mss_lock);
 
 	return mss_index;
 }