Wrong status returned to the server if deployment_status callback fails

If the deployment status is success but that the `deployment_status` callback fails (it is used in mender-stm32l4a6-zephyr-example to load modules), then the status reported to the server is `success` and doesn't take care of callback result.

To be decided if this is a bug or not because this is specific to an example at the moment, not sure it's a real use case.