perf trace: fix return value printing for set_robust_list and rseq

JIRA: https://issues.redhat.com/browse/RHEL-78308

• Ensure return value always gets printed, even if no errpid is returned
• Fix the definitions of set_robust_list and rseq to show they do not return a pid.

Signed-off-by: Anubhav Shelat ashelat@redhat.com