Integer splats should use an operand when a register is not allocated.

Bug: V8:8927
Change-Id: I14c80b7b073fae3754ec32f4fa8605af399ef341
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1513102Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60138}