migration: finalize current_migration object

current_migration has .instance_finalize callback, but it is not
called, because nobody unrefs current_migration. Fix that.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
diff --git a/vl.c b/vl.c
index 444b750..f1c52fe 100644
--- a/vl.c
+++ b/vl.c
@@ -4792,6 +4792,7 @@
     monitor_cleanup();
     qemu_chr_cleanup();
     user_creatable_cleanup();
+    migration_object_finalize();
     /* TODO: unref root container, check all devices are ok */
 
     return 0;