[clang] [clang-tools-extra] [llvm] [mlir] [NFC] Fix spelling of definition in comments (PR #208138)

[via llvm-commits]

divedb wrote:

I have read the LLVM contribution policies, including the LLVM AI Tool Use Policy. No AI tools were used for this change.

https://github.com/llvm/llvm-project/pull/208138