[llvm] [MachinePipeliner] Fix MachineMemOperand to be cleared when update fails (PR #80841)

[Yuta Mukai via llvm-commits]

ytmukai wrote:

> However, it assumes that the alignment is guaranteed if MachineMemOperand does not exist or has an invalid value, which appears to be a problem.
> I will propose a modification that would determine it more conservatively.

I created this patch and posted a new PR #83948.

https://github.com/llvm/llvm-project/pull/80841