[llvm] [Mips] Fix missing sign extension in expansion of sub-word atomic max (PR #77072)

[via llvm-commits]

yingopq wrote:

> @yingopq As I understand it, this was reproduced with the release/18.x branch (or rust's fork, which is essentially the same), which already contains that second commit as well.

In https://github.com/rust-lang/rust/issues/123772, he comments ```With src/llvm-project pointing to https://github.com/llvm/llvm-project/commit/fbb27d16fa12aa595cbd20a1fb5f1c5b80748fa4 the test also fails, but when pointing src/llvm-project to the parent commit (https://github.com/llvm/llvm-project/commit/e74c1678231ab2a7c6defe8bb90366e664780d6f) the test passes.```. So I reply him use code 0e501dbd932ef1c6f4e747c83bf33beef0a09ecf

https://github.com/llvm/llvm-project/pull/77072