vhost: copy_to_user -> __copy_to_user

We do access_ok checks at setup time, so we don't need to
redo them on each access.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/vhost.c

@@ -1258,7 +1258,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
 
 	start = vq->last_used_idx % vq->num;
 	used = vq->used->ring + start;
-	if (copy_to_user(used, heads, count * sizeof *used)) {
+	if (__copy_to_user(used, heads, count * sizeof *used)) {
 		vq_err(vq, "Failed to write used");
 		return -EFAULT;
 	}