[llvm] [TableGen][DecoderEmitter] Resolve a FIXME in emitDecoder (PR #154649)

[Rahul Joshi via llvm-commits]

https://github.com/jurahul approved this pull request.

LGTM, but can you wait for someone from M68k side to approve as well?

https://github.com/llvm/llvm-project/pull/154649