Many, if not most, distributions these days put /dev on a ramdrive and use udev to populate it. When your system powers down, the ramdrive and any changes you made to it will be lost. The proper way to handle this is to instead add a udev rule
so that it will create the symlink you want automatically.
You could also simply change the device that xine uses in its configuration options instead. It's available in the "media" tab, although you have to change the experience level to advanced or higher before it becomes available.