nir: Do not reset shared_size in nir_lower_io.

I'd like to use raw shared intrinsics already for some raytracing
stuff before this pass gets called and this was a real pitfall.

This mirrors scratch_size and constant_data_size.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10094>

src/compiler/nir/nir_lower_io.c

@@ -2249,7 +2249,7 @@ lower_vars_to_explicit(nir_shader *shader,
       offset = shader->scratch_size;
       break;
    case nir_var_mem_shared:
-      offset = 0;
+      offset = shader->info.shared_size;
       break;
    case nir_var_mem_constant:
       offset = shader->constant_data_size;