meson/megadriver: replace hardlinks with symlinks

The wording in the script has always (3218056e) been about symlinks, and it feels like the use of link() instead of symlink() was a typo that became fact.

These hardlinks make packaging harder (many distros have some variant of this patch locally) especially when it comes to debug packages where gdb expects the symbols file to have the same name as the lib the symbols come from, and I don't think they make anything better, so let's change to code to match the documentation :)