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/migration/migration.c b/migration/migration.c
index 17cc219..7a77b19 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -132,6 +132,11 @@
     }
 }
 
+void migration_object_finalize(void)
+{
+    object_unref(OBJECT(current_migration));
+}
+
 /* For outgoing */
 MigrationState *migrate_get_current(void)
 {