This line:
$('#prid').value=ui.item.value;
Should Be:
$('#prid').val(ui.item.value);
In addition if you want the original input box to display the selected item you would need:
select: function( event, ui ) {
event.preventDefault();
$("#search").val(ui.item.label);
PK.render(ui.item.value);
}
Updated JSFiddle