displaytitle: Pass-by-reference fix for PHP 5.4

PHP 5.4 includes some pass-by-reference changes which apparently make
the '&' sigil necessary here.

Spotted by Mormegil <mormegil@centrum.cz>. Followup to Ie162535b.

Change-Id: I038fa7f8e1559c95dba7b9b498fc1d1f5eb76887
Merge "displaytitle: Pass-by-reference fix for PHP 5.4"