The computation to find the hash entry is already performed on Word64,
and the actual value access later is also performed on Word64 indices,
so there's no point to go to Word32 in between.

Bug: v8:8015, v8:8178
Change-Id: I160e02166beceb79dcc8e69f9c365871a4c42606
Reviewed-on: https://chromium-review.googlesource.com/1226648Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55950}