emit_u32_to_intptr should zero-extend the low 32 bits of the src.

Bug: v8:10925
Change-Id: I48135da054d5f30d7aa4d67918c839debc7cdb2f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2418031Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Cr-Commit-Position: refs/heads/master@{#70024}