[BUGFIX] Use correct property for images in FrontendUser

As the image field has been changed to FAL, also the model must
be adopted.

Resolves: #80437
Releases: master
Change-Id: I09b6ef8db190467ee5dfea67e5e66ded12b99dcd
Reviewed-on: https://review.typo3.org/52146


Tested-by: TYPO3com <no-reply@typo3.com>
Tested-by: Nikolai Townsend <info@nikolaitownsend.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>