virtio-blk: add missing virtio_detach_element() call

Make sure to unmap the scatter-gather list and decrement vq->inuse
before freeing requests in virtio_blk_reset().
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NLadi Prosek <lprosek@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/block/virtio-blk.c

@@ -665,6 +665,7 @@ static void virtio_blk_reset(VirtIODevice *vdev)
     while (s->rq) {
         req = s->rq;
         s->rq = req->next;
+        virtqueue_detach_element(req->vq, &req->elem, 0);
         virtio_blk_free_request(req);
     }