Correct the test expect result as the spec specifies the accumulator is 2*SEW
bits. Fix the simulator implementation as well.

R=qiuji@iscas.ac.cn

Change-Id: Ia5d11b3214cf32635c3767df75992b2a50ee6980
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3878452
Commit-Queue: Yahan Lu <yahan@iscas.ac.cn>
Reviewed-by: Yahan Lu <yahan@iscas.ac.cn>
Cr-Commit-Position: refs/heads/main@{#83354}