intel/fs: Alloc pull constants off mem_ctx

It doesn't actually matter since the only user of push constants, i965,
ralloc_steals it back to NULL but it's more consistent and probably
fixes memory leaks in some error cases.

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

src/intel/compiler/brw_fs.cpp

@@ -2095,7 +2095,7 @@ fs_visitor::assign_constant_locations()
    stage_prog_data->param = ralloc_array(mem_ctx, uint32_t, num_push_constants);
    if (num_pull_constants > 0) {
       stage_prog_data->nr_pull_params = num_pull_constants;
-      stage_prog_data->pull_param = ralloc_array(NULL, uint32_t,
+      stage_prog_data->pull_param = ralloc_array(mem_ctx, uint32_t,
                                                  num_pull_constants);
    }