c564841fae
color/zs are stored in a union so testing for zs.stencil_offset
isn't the correct way to test for stencil.
Fixes: 988f148db3 ("ac/surface: overlap color and Z/S fields using a union in gfx9_surf_layout")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11625>