added a missing phpdoc param

src/Symfony/Bridge/Doctrine/Form/ChoiceList/EntityChoiceList.php

@@ -91,6 +91,7 @@ class EntityChoiceList extends ObjectChoiceList
      * @param string                $labelPath         The property path used for the label
      * @param EntityLoaderInterface $entityLoader      An optional query builder
      * @param array                 $entities          An array of choices
+     * @param array                 $preferredEntities An array of preferred choices
      * @param string                $groupPath         A property path pointing to the property used
      *                                                 to group the choices. Only allowed if
      *                                                 the choices are given as flat array.