anv/pipeline: Call nir_lower_system_valaues after brw_preprocess_nir

We currently have a bug where nir_lower_system_values gets called before
nir_lower_var_copies so it will miss any system value uses which come
from a copy_var intrinsic.  Moving it to after brw_preprocess_nir fixes
this problem.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: mesa-stable@lists.freedesktop.org

src/intel/vulkan/anv_pipeline.c

@@ -188,13 +188,14 @@ anv_shader_compile_to_nir(struct anv_pipeline *pipeline,
    NIR_PASS_V(nir, nir_propagate_invariant);
    NIR_PASS_V(nir, nir_lower_io_to_temporaries,
               entry_point->impl, true, false);
-   NIR_PASS_V(nir, nir_lower_system_values);
 
    /* Vulkan uses the separate-shader linking model */
    nir->info.separate_shader = true;
 
    nir = brw_preprocess_nir(compiler, nir);
 
+   NIR_PASS_V(nir, nir_lower_system_values);
+
    if (stage == MESA_SHADER_FRAGMENT)
       NIR_PASS_V(nir, anv_nir_lower_input_attachments);