hv_netvsc: Fix a warning of suspicious RCU usage

This fixes a warning of "suspicious rcu_dereference_check() usage"
when nload runs.

Fixes: 776e726b ("netvsc: fix RCU warning in get_stats")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/netvsc_drv.c

@@ -1239,12 +1239,15 @@ static void netvsc_get_stats64(struct net_device *net,
 			       struct rtnl_link_stats64 *t)
 {
 	struct net_device_context *ndev_ctx = netdev_priv(net);
-	struct netvsc_device *nvdev = rcu_dereference_rtnl(ndev_ctx->nvdev);
+	struct netvsc_device *nvdev;
 	struct netvsc_vf_pcpu_stats vf_tot;
 	int i;
 
+	rcu_read_lock();
+
+	nvdev = rcu_dereference(ndev_ctx->nvdev);
 	if (!nvdev)
-		return;
+		goto out;
 
 	netdev_stats_to_stats64(t, &net->stats);
 
@@ -1283,6 +1286,8 @@ static void netvsc_get_stats64(struct net_device *net,
 		t->rx_packets	+= packets;
 		t->multicast	+= multicast;
 	}
+out:
+	rcu_read_unlock();
 }
 
 static int netvsc_set_mac_addr(struct net_device *ndev, void *p)