Use pointer arithmetic to go back to the first nodes_ element
instead of computing the address manually.

Bug: none
Change-Id: I887c41908dc6891ed15aa03698ca2305924dcab2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2512904Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70913}