praudit(1): return 0 on success

Cherry pick https://github.com/openbsm/openbsm/commit/ed83bb3

Submitted by: aniketp
Reviewed by: rwatson, 0mp
Obtained from: OpenBSM
MFC after: 2 weeks
Sponsored by: Google, Inc. (GSoC 2018)
Pull Request: https://github.com/openbsm/openbsm/pull/32