Sorry, the docs is incorrect. The submitted post ID is added separately as the 2nd parameter of the hook. Please change the code to this:
add_action ('rwmb_frontend_after_process','emnsh_rwmb_frontend_after_process', 10, 2);
function emnsh_rwmb_frontend_after_process($config, $post_id) {
if ($post_id') {
$name = rwmb_meta('emnsh-name');
wp_update_post(array(
'ID' => $config['post_id'],
'post_title'=>$name
));
}
}
I also updated the docs.