It turns out that because we are *subtracting* from fp, we need to
*subtract less* to get a higher address. Who knew.

R=jkummerow@chromium.org

Bug: v8:9830, chromium:1014798
Change-Id: I5b9782dd0be27f4c3efbd306ec6c3450b249cb55
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1864933Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64321}