[BUGFIX] Correct permissions for root page setting up empty site

Use the correct maximal permission "31" for the root page when setting
up an empty site during the installation process instead of "32" which
leads to non-editable permissions for that page even by an admin.

Resolves: #83369
Releases: master, 8.7, 7.6
Change-Id: I092f32b48c2a6deb79727fd6a1f8730829161287
Reviewed-on: https://review.typo3.org/55246


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>