[clang] [CIR][NFC] Update existing atomic ops to match assembly conventions (PR #161543)

[Bruno Cardoso Lopes via cfe-commits]

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

Good catch! LGTM - perhaps this is more NFCI than NFC? Seems like it's fixing some parser bugs?

https://github.com/llvm/llvm-project/pull/161543