[BUGFIX] Add missing namespacing for calling GeneralUtility

Regression-fix for change from:
https://review.typo3.org/25057

Resolves: #54117
Releases: 6.1, 6.0
Change-Id: I0de156365d4d8f55cb269e0b29e40b7c3dbcf9e5
Reviewed-on: https://review.typo3.org/25829
Reviewed-by: Steffen Ritter
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Oliver Klee
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel