[BUGFIX] Fix wrong path in EXT:cms/ext_autoload.php

One path is wrong in ext_autoload and should be fixed

Change-Id: I8a84ed8bec8f877dee491127c43ffa5ca0bc3757
Fixes: #37478
Releases: 6.0
Reviewed-on: http://review.typo3.org/13837
Reviewed-by: Wouter Wolters
Reviewed-by: Ingo Renner
Tested-by: Ingo Renner