softmmu/qdev-monitor: fix use-after-free in qdev_set_id()

Reported by Coverity (CID 1465222).

Fixes: 4a1d9377 ("softmmu/qdev-monitor: add error handling in qdev_set_id")
Cc: Damien Hedde <damien.hedde@greensocs.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20211102163342.31162-1-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20211115145409.176785-14-kwolf@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>