[clang] [CIR] Change CmpOp assembly format to use bare keyword style (PR #185114)

[Henrich Lauko via cfe-commits]

xlauko wrote:

> I have no problems/concerns if others are on board. I'm not really opinionated one way or another on the change though, so I'd like to hear from @andykaylor and @bcardosolopes

@erichkeane this follows our [style guide](https://llvm.github.io/clangir/Dialect/cir-style-guide.html#arguments-list). I believe written by @bcardosolopes long time ago. And my thinking is lets try to align as much as possible before CIR starts to be used downstream and each such change will be hard to pass.

https://github.com/llvm/llvm-project/pull/185114