Make hosting_https_update_7001 PHP 5.3 compatible

hosting_https_update_7001 does: $field = hosting_https_schema()['hosting_https_site']['fields']['client_authentication']; however array access from a function return is only supported in PHP 5.4+

I think Aegir still supporting PHP 5.3 just like Drupal 7 core? We still have an Aegir box on 5.3 floating around and everything else is 5.3 compatible, makes sense that hosting_https should be too.