[llvm] [MIPS][ISel] Fix musttail (PR #161860)

[Djordje Todorovic via llvm-commits]

djtodoro wrote:

> Please squash changes into initial commit

Per "Contributing to LLVM" Policy, we do not do force-push (and squash), we rather use incremental changes to address comments during review process. And, once the pull request is approved, we select the “Squash and merge” button.

https://github.com/llvm/llvm-project/pull/161860