In atomic.wait we overwrote the register which stored the index,
without checking if it was still in use or not.

R=clemensb@chromium.org

Bug: v8:10898
Change-Id: Iab6e1a84c71887af81d307c4ca795109ce2fdfc2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2428928
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70134}