There is no need for write barriers if the stored value is known to be a
Smi.

R=thibaudm@chromium.org

Bug: v8:11453
Change-Id: Id1cf306b246686c245d1be5f72c46b54ba9829ca
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2707172Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72903}