[BUGFIX] BackendUtility should be called staticly

There are same BackendUtility calls, that are not static.
Utility calls should always be staticly.

Change-Id: Ifa796cf29eaa6688a8123a57ce760c77a2bc6dbb
Reviewed-on: https://review.typo3.org/31033
Reviewed-by: Jo Hasenau
Tested-by: Jo Hasenau