<?php
add_action("gform_pre_render", "set_chosen_options");
function set_chosen_options($form){
    ?>

    <script type="text/javascript">
        gform.addFilter('gform_chosen_options','set_chosen_options_js');
        //limit how many options may be chosen in a multi-select to 2
        function set_chosen_options_js(options, element){
            //form id = 85, field id = 5
            if (element.attr('id') == 'input_85_5'){
                options.max_selected_options = 2;
            }

            return options;
        }
    </script>

    <?php
    //return the form object from the php hook
    return $form;
}
?>