[llvm] [MIPS] Fix missing ANDI optimization (PR #97689)

[Alexander Richardson via llvm-commits]

arichardson wrote:

> > I don't work on MIPS anymore but this looks correct to me.
> > One nit: I think it would be good to pre-commit the test with the existing codegen first and then have this patch show the codegen improvement.
> 
> Yes, this would be best. Thanks! Need I split it into two patches and resubmit again?

You could commit the baseline test directly and then just update this pull request.

https://github.com/llvm/llvm-project/pull/97689