[BUGFIX] Fixed wrong extkey in TypoScriptUtility

Change-Id: I41a31dc0611fd17a7aceef214f6520e6dd8eb1d0
Reviewed-on: http://review.typo3.org/32352
Reviewed-by: Armin Ruediger Vieweg <armin@v.ieweg.de>
Tested-by: Armin Ruediger Vieweg <armin@v.ieweg.de>