qdev: Fix use after free in qdev_init_nofail error path

Since 69382d8b (qdev: Fix object reference leak in case device.realize()
fails), object_property_set_bool could release the object. The error
path wants the type name, so hold an reference before realizing it.

Cc: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: NFam Zheng <famz@redhat.com>
Message-Id: <1470109301-12966-1-git-send-email-famz@redhat.com>
Reviewed-by: NJohn Snow <jsnow@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/core/qdev.c

@@ -354,12 +354,14 @@ void qdev_init_nofail(DeviceState *dev)
 
     assert(!dev->realized);
 
+    object_ref(OBJECT(dev));
     object_property_set_bool(OBJECT(dev), true, "realized", &err);
     if (err) {
         error_reportf_err(err, "Initialization of device %s failed: ",
                           object_get_typename(OBJECT(dev)));
         exit(1);
     }
+    object_unref(OBJECT(dev));
 }
 
 void qdev_machine_creation_done(void)