vdpa_sim_blk: call vringh_complete_iotlb() also in the error path

Call vringh_complete_iotlb() even when we encounter a serious error
that prevents us from writing the status in the "in" header
(e.g. the header length is incorrect, etc.).

The guest is misbehaving, so maybe the ring is in a bad state, but
let's avoid making things worse.

Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20220630153221.83371-4-sgarzare@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>