virtio_net: Replace deprecated CPU-hotplug functions.

The functions get_online_cpus() and put_online_cpus() have been
deprecated during the CPU hotplug rework. They map directly to
cpus_read_lock() and cpus_read_unlock().

Replace deprecated CPU-hotplug functions with the official version.
The behavior remains unchanged.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/virtio_net.c

@@ -2197,14 +2197,14 @@ static int virtnet_set_channels(struct net_device *dev,
 	if (vi->rq[0].xdp_prog)
 		return -EINVAL;
 
-	get_online_cpus();
+	cpus_read_lock();
 	err = _virtnet_set_queues(vi, queue_pairs);
 	if (err) {
-		put_online_cpus();
+		cpus_read_unlock();
 		goto err;
 	}
 	virtnet_set_affinity(vi);
-	put_online_cpus();
+	cpus_read_unlock();
 
 	netif_set_real_num_tx_queues(dev, queue_pairs);
 	netif_set_real_num_rx_queues(dev, queue_pairs);
@@ -2959,9 +2959,9 @@ static int init_vqs(struct virtnet_info *vi)
 	if (ret)
 		goto err_free;
 
-	get_online_cpus();
+	cpus_read_lock();
 	virtnet_set_affinity(vi);
-	put_online_cpus();
+	cpus_read_unlock();
 
 	return 0;