Form element validation handler; Stores the new values in the form state.
entity_reference_field_instance_settings_form()
function _entity_reference_field_instance_settings_validate($form, &$form_state) {
$instance = $form['#instance'];
if (isset($form_state['values']['instance'])) {
$instance['settings'] = $form_state['values']['instance']['settings'];
}
$form_state['entity_reference']['instance'] = $instance;
unset($form_state['values']['instance']['settings']['handler_submit']);
}