[clang] [CIR] Fix building ClangIR after RegionBranchOpInterface revamp (PR #165441)

[Mehdi Amini via cfe-commits]

================
@@ -42,7 +44,8 @@ void LoopOpInterface::getLoopOpSuccessorRegions(
   }
 
   // Branching from step: go to condition.
-  if (op.maybeGetStep() == point.getRegionOrNull()) {
+  if (op.maybeGetStep() ==
+      point.getTerminatorPredecessorOrNull()->getParentRegion()) {
----------------
joker-eph wrote:

```suggestion
  if (op.maybeGetStep() == parentRegion) {
```

https://github.com/llvm/llvm-project/pull/165441