Add const values 'nRows' and 'nCols'

Summary: Replace the previous usages of integer 8 with 'nRows' and 'nCols'.

Reviewers: KDE Games, aacid

Reviewed By: aacid

Subscribers: aacid, chehrlic, kde-games-devel

Differential Revision: https://phabricator.kde.org/D27105