[#33150] Use data-direction attribute to update direction

When we update direction, the default `newDirection` variable is 'ASC', but it will cause the wrong direction if we didn't  write ordering options in `filter.xml`, the auto generated ordering option in `list[fullordering]` will cause grid not sortable in `DESC`.

I changed it to get data from `data-direction` and it working fine now.

Tracker: http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33150&start=0