virtio-iommu: Fix coverity issue in virtio_iommu_handle_command()

Coverity points out (CID 1430180) that the new case is missing
break or a /* fallthrough */ comment. Break is the right thing to
do as in that case, tail is not used.

Fixes 1733eebb ("virtio-iommu: Implement RESV_MEM probe request")
Signed-off-by: NEric Auger <eric.auger@redhat.com>
Reported-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 20200708160147.18426-1-eric.auger@redhat.com
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/virtio/virtio-iommu.c

@@ -534,6 +534,7 @@ static void virtio_iommu_handle_command(VirtIODevice *vdev, VirtQueue *vq)
             ptail = (struct virtio_iommu_req_tail *)
                         (buf + s->config.probe_size);
             ptail->status = virtio_iommu_handle_probe(s, iov, iov_cnt, buf);
+            break;
         }
         default:
             tail.status = VIRTIO_IOMMU_S_UNSUPP;