intel/nir: Stop returning the shader from helpers

Now that NIR_TEST_* doesn't swap the shader out from under us, it's
sufficient to just modify the shader rather than having to return in
case we're testing serialization or cloning.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/intel/compiler/brw_vec4_gs_visitor.cpp

@@ -639,10 +639,10 @@ brw_compile_gs(const struct brw_compiler *compiler, void *log_data,
                        &c.input_vue_map, inputs_read,
                        shader->info.separate_shader);
 
-   shader = brw_nir_apply_sampler_key(shader, compiler, &key->tex, is_scalar);
+   brw_nir_apply_sampler_key(shader, compiler, &key->tex, is_scalar);
    brw_nir_lower_vue_inputs(shader, &c.input_vue_map);
    brw_nir_lower_vue_outputs(shader);
-   shader = brw_postprocess_nir(shader, compiler, is_scalar);
+   brw_postprocess_nir(shader, compiler, is_scalar);
 
    prog_data->base.clip_distance_mask =
       ((1 << shader->info.clip_distance_array_size) - 1);