tg3: fix return value in tg3_get_stats64

When tp->hw_stats is 0, tg3_get_stats64 should display previously
recorded stats. So it returns &tp->net_stats_prev. But the caller,
dev_get_stats, ignores the return value.

Fix this by assigning tp->net_stats_prev to stats and returning stats.
Signed-off-by: NGovindarajulu Varadarajan <_govind@gmx.com>
Acked-by: NPrashant Sreedharan <prashant@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/tg3.c

@@ -14093,8 +14093,9 @@ static struct rtnl_link_stats64 *tg3_get_stats64(struct net_device *dev,
 
 	spin_lock_bh(&tp->lock);
 	if (!tp->hw_stats) {
+		*stats = tp->net_stats_prev;
 		spin_unlock_bh(&tp->lock);
-		return &tp->net_stats_prev;
+		return stats;
 	}
 
 	tg3_get_nstats(tp, stats);