[llvm] [GlobalISel] Fixes unused variable error in testMOPredicate_MO (PR #143364)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-aarch64-darwin` running on `doug-worker-5` while building `llvm` at step 4 "cmake-configure".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/190/builds/21122

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 4 (cmake-configure) failure: cmake (failure)


```

</details>

https://github.com/llvm/llvm-project/pull/143364