go/token: simplify fixOffset
Each time I go to definition of this I am deeply confused
at what I am looking, so let's clean this a bit with modern Go.
Change-Id: I8f44e78f0cdde9b970388f9b98a2720e6a6a6964
Reviewed-on: https://go-review.googlesource.com/c/go/+/738341
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>