fixes memory leak in func_audiohookinherit.c

(closes issue #15394)
Reported by: boroda
Patches:
      bug15394_memoryleak_diff2.txt uploaded by dbrooks (license 790)
Tested by: dbrooks, boroda



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@228268 65c4cc65-6c06-0410-ace0-fbb531ad65f3