DAOS-19385 rebuild: fix return code (#18761)

[NiuYawei]

Return proper error code instead of 0 in migrate_pool_tls_create().

Steps for the author:

• Commit message follows the guidelines.
• Appropriate Features or Test-tag pragmas were used.
• Appropriate Functional Test Stages were run.
• At least two positive code reviews including at least one code owner from each category referenced in the PR.
• Testing is complete. If necessary, forced-landing label added and a reason added in a comment.

After all prior steps are complete:

• Gatekeeper requested (daos-gatekeeper added as a reviewer).

[github-actions]

Ticket title is '2.8rc2: seg fault during reintegration - daos_srv/libobj.so(ds_migrate_object+0x440) [0x7f66981f55d0] '
Status is 'Open'
Labels: 'test_2.8.0rc'
https://daosio.atlassian.net/browse/DAOS-19385