[llvm] [mlir] [MLIR][TableGen] Minor code cleanup in DirectiveCommonGen (PR #110290)

[Valentin Clement バレンタイン クレメン via llvm-commits]

https://github.com/clementval commented:

Looks like the pre ci is red. I don't know if this is related to this patch but please have a look. 

https://github.com/llvm/llvm-project/pull/110290