Use ast_free() instead of free().

(closes issue #11309)
Reported by: Laureano
Patches: 
      res_odbc.c.patch uploaded by Laureano (license 265)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@91131 65c4cc65-6c06-0410-ace0-fbb531ad65f3