vhost_net: make vhost_zerocopy_signal_used() return void

None of its caller use its return value, so let it return void.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/vhost/net.c

@@ -276,7 +276,7 @@ static void copy_iovec_hdr(const struct iovec *from, struct iovec *to,
  * of used idx. Once lower device DMA done contiguously, we will signal KVM
  * guest used idx.
  */
-static int vhost_zerocopy_signal_used(struct vhost_net *net,
+static void vhost_zerocopy_signal_used(struct vhost_net *net,
 				       struct vhost_virtqueue *vq)
 {
 	struct vhost_net_virtqueue *nvq =
@@ -297,7 +297,6 @@ static int vhost_zerocopy_signal_used(struct vhost_net *net,
 	}
 	if (j)
 		nvq->done_idx = i;
-	return j;
 }
 
 static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)