Coverity rightly reports that is not free in that case.

Fixes: Coverity CID 1487559
Fixes: 100890f7 ("vhost: Shadow virtqueue buffers forwarding")

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20220512175747.142058-7-eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>