[PATCH] qom: fix refcounting in object_property_del_child()

Start VM with 8 multiple-function block devs, hot-removing
those block devs by 'device_del ...' would cause qemu abort.

object_ref() is called in object_property_add_child(),
but we don't unref it in object_property_del_child().

| (qemu) device_del virti0-0-0
| (qemu) **
| ERROR:qom/object.c:389:object_delete: assertion failed: (obj->ref == 0)

Signed-off-by: Amos Kong <akong <at> redhat.com>
---
 qom/object.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/qom/object.c b/qom/object.c
index e721fc2..9da6b59 100644
--- a/qom/object.c
+++ b/qom/object.c
 <at>  <at>  -320,6 +320,7  <at>  <at>  static void object_property_del_child(Object *obj, Object *child, Error **errp)
     QTAILQ_FOREACH(prop, &obj->properties, node) {
         if (strstart(prop->type, "child<", NULL) && prop->opaque == child) {
             object_property_del(obj, prop->name, errp);
+            object_unref(child);
             break;
         }
     }