Fix additional memory leak in process_mapfile

[bret_ketchum_dell.com]

Summary

Additional Coverity detected memory leak fix.

[cem]

Thanks.

lib/libpmc/pmu-events/jevents.c

783–806 ↗

(On Diff #77136)

If goto out is acceptable at ~786, maybe we can just do that here too and use a variable for the return value. This fix seems ok as-is, though. Either way.