Fix documentation error when validating the xml in trunk caused by r375150.
Moved the description end tag down to below the variablelist element end tag.

Found when compiling with --dev-mode-enabled.

(issue ASTERISK-20289)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@375215 65c4cc65-6c06-0410-ace0-fbb531ad65f3