[clang] [CIR] Simplify ConstantOp accesses and its getDefiningOp (PR #151216)

[Henrich Lauko via cfe-commits]

xlauko wrote:

### Merge activity

* **Aug 1, 6:06 PM UTC**: [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/151216) rebased this pull request as part of a merge.


https://github.com/llvm/llvm-project/pull/151216