Refactor: tools: Improve loop bounds in crm_error

256 is still a magic number for the top end of pcmk_result_pcmk_rc, but
there is not a reliable max system errno AFAIK. For example, see the
#ifdef __hppa__ block in results.h -- such systems may have error
codes above 200 (PCMK_CUSTOM_OFFSET, which we used as the max before).

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>