virtio-blk: blockdev_mark_auto_del is transport-independent

Move it from virtio_blk_exit_pci to virtio_blk_exit.

This is included here because the next patch removes proxy->block.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/virtio-blk.c

@@ -621,5 +621,6 @@ void virtio_blk_exit(VirtIODevice *vdev)
 {
     VirtIOBlock *s = to_virtio_blk(vdev);
     unregister_savevm(s->qdev, "virtio-blk", s);
+    blockdev_mark_auto_del(s->bs);
     virtio_cleanup(vdev);
 }

hw/virtio-pci.c

@@ -726,7 +726,6 @@ static int virtio_blk_exit_pci(PCIDevice *pci_dev)
 
     virtio_pci_stop_ioeventfd(proxy);
     virtio_blk_exit(proxy->vdev);
-    blockdev_mark_auto_del(proxy->block.bs);
     return virtio_exit_pci(pci_dev);
 }