res_config_mysql: Fix Setting The Column Name Incorrectly

When support for a realtime sorcery module was added in revision 386731, the
wrong property was accidentally used for setting the column name to be updated
in the database table.  This patch fixes the typo.

(closes issue ASTERISK-23177)
Reported by: Denis
Tested by: Denis
Patches:
    asterisk-23177-use-field-name.diff by Michael L. Young (license 5026)


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@406311 f38db490-d61c-443f-a65b-d21fe96a405b