The map in the cache is the LHS, not the RHS.

Change-Id: Idf6b4fafc8c62aea5b8f5f55258241939cf9829d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1667410Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62289}