Fix lowering of functions that returns the result of an
i8x16 or i16x8 operation.

Bug: v8:10507
Change-Id: Ia3b29e69cff7771f85dc5160937cbaf2bbc12b55
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2399049
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69832}