Fixes dEQP-VK.mesh_shader.ext.misc.custom_attributes*.
Fixes: 16c7c37718 ("anv: move preprocessing of NIR right before compilation")
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22629>