This CL fixes the "sort-lengths" benchmark so the ElementsKind of the
array to sort is PACKED_SMI again. This was somehow broken.

R=jgruber@chromium.org

Change-Id: I129e001eae4c88e9f99174b3494193232d933c3f
Reviewed-on: https://chromium-review.googlesource.com/1188122Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Simon Zünd <szuend@google.com>
Cr-Commit-Position: refs/heads/master@{#55371}