The function being called is directly above this declaration. It's a static function not used outside of this file. What are the chances that someone would edit this code without understanding what "three" is used for in this context? Pretty slim I wager.

It's good that people are auditing the linux source code but if you stumble upon some weird looking code (which again, is not the case here in my opinion) the right way to deal with it is not to post it on hacker news. Contact the maintainer (look at the MAINTAINER file at the root of the kernel) if possible with a patch to fix the issue.