Fix return type on hpcrun_retry_libunw_find_step.
Fix return type on hpcrun_retry_libunw_find_step.

HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit