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: Fam Zheng <famz@redhat.com>
Message-Id: <1470109301-12966-1-git-send-email-famz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
