<?php 


function custom_em_multiple_booking_get_admin_url( $admin_url, $EM_Multiple_Booking ){
  $admin_url = em_add_get_params($admin_url, array('post_type'=>'event') );
  return $admin_url;
}
add_filter('em_multiple_booking_get_admin_url','custom_em_multiple_booking_get_admin_url', 100, 2);