Fixes QSCustomizer header height

So that the tiles in QSCustomizer align with the real tiles in portrait.
Fixed the comment specifying how to calculate the proper height based on
the views in QSPanel and QSCustomizer.

Test: visual. It matches.
Test: change display and font size. It still matches.
Fixes: 132813963
Change-Id: I93a3531ab8e6170fb2665552ce3d909533337301