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

[David Green via llvm-commits]

davemgreen wrote:

I'm not sure if the pipeliner is correct or not, but would it be possible to fix this in the load/store optimizer? It looks like it should be checking that the size is not unknown (or not converting to an Align and back?)

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