ac/surface: fix CMASK fast clear for NPOT textures with mipmapping on SI/CI/VI

This fixes VM faults and corruption.

Cc: 18.1 18.2 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
(cherry picked from commit 1e40f694)