Fix retvals for DetectTargetParse

[jsoref]

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• [x] I have read the contributing guide lines at https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Contributing
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Link to redmine ticket:

Describe changes:

• Fixing docs for DetectTargetParse

#suricata-verify-pr: #suricata-verify-repo: #suricata-verify-branch: #suricata-update-pr: #suricata-update-repo: #suricata-update-branch: #libhtp-pr: #libhtp-repo: #libhtp-branch:

[jlucovsky]

Thanks for the contribution.

In https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Code_Submission_Quality_Criteria we list commit message hints, including the main commit message be something like have a prefix and subsystem, e.g., "detect: function header return value clarification"

[victorjulien]

Merged in #7839, thanks!