Demos: Listview: Fixed a typo arrow-r for the default icon value.

This is simple pull request.

The default icons changed from arrow to carat in commit https://github.com/jquery/jquery-mobile/commit/56c15c70df9651c011c2f41b5bba054b47142ba9.
But I think that Listview demo has not been updated yet. 
So, I changed "arrow-r" to "carat-r".