We can use r0 itself without the need of loading it with "0",
if it is used as the first input of MemOperand.

Change-Id: I71aafea8bba098f925c55eb9127c6b37ac37cb7b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2332864
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#69232}