nir/builder: Drop the mem_ctx arg from nir_builder_init_simple_shader().

This looks a lot more simple now!

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7323>

src/intel/compiler/brw_nir.c

@@ -1475,7 +1475,7 @@ brw_nir_create_passthrough_tcs(void *mem_ctx, const struct brw_compiler *compile
                                const nir_shader_compiler_options *options,
                                const struct brw_tcs_prog_key *key)
 {
-   nir_builder b = nir_builder_init_simple_shader(NULL, MESA_SHADER_TESS_CTRL,
+   nir_builder b = nir_builder_init_simple_shader(MESA_SHADER_TESS_CTRL,
                                                   options);
    ralloc_adopt(mem_ctx, b.shader);
    nir_shader *nir = b.shader;