virtio_balloon: remove the unnecessary 0-initialization

We've changed to kzalloc the vb struct, so no need to 0-initialize
this field one more time.
Signed-off-by: NWei Wang <wei.w.wang@intel.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NCornelia Huck <cohuck@redhat.com>

drivers/virtio/virtio_balloon.c

@@ -925,7 +925,6 @@ static int virtballoon_probe(struct virtio_device *vdev)
 						  VIRTIO_BALLOON_CMD_ID_STOP);
 		vb->cmd_id_stop = cpu_to_virtio32(vb->vdev,
 						  VIRTIO_BALLOON_CMD_ID_STOP);
-		vb->num_free_page_blocks = 0;
 		spin_lock_init(&vb->free_page_list_lock);
 		INIT_LIST_HEAD(&vb->free_page_list);
 		if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {