qom: fix leak for objects created with -object The object must be unref-ed when its variable goes out of scope. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Igor Mammedov <imammedo@redhat.com> Tested-by: Igor Mammedov <imammedo@redhat.com> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>