[llvm] [Mips] Add the missing judgment when processing function handleMFLOSlot (PR #121463)

[via llvm-commits]

yingopq wrote:

> I guess that there may be some other problem: why this patch can effects MIPSr2? I guess that the default port of FreeBSD is r2？

We have already made a restriction at the beginning.
```
if (STI->hasMips32() || STI->hasMips5())
    return false;
```

https://github.com/llvm/llvm-project/pull/121463