Sorry, that last line should read:
echo '<a href="'.get_permalink($post->post_parent).'">'.get_the_title($post->post_parent).'</a>';
That’s a roundabout way of doing it; try this:
if(intval($post->post_parent)>0)
{
while(intval($post->post_parent)>0)
$post = get_post($post->post_parent);
}
echo '<a href="'.get_permalink($post->post_parent).'">'.get_the_title($post->post_parent).'</a>';
