radv: Fix CMASK dimensions.

Mirrors

1e40f694 "ac/surface: fix CMASK fast clear for NPOT textures with mipmapping on SI/CI/VI"

CC: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
(cherry picked from commit 233718a1)