[Coroutines] Fix incorrect attribute name coroutine.presplit (NFC) (#78296)

Those are probably leftovers from an old name of the same attribute.
Fixed for the sake of consistency.

Co-authored-by: Yoni Lavi <[email protected]>

Author: yonillasky

llvm/lib/Transforms/Coroutines/CoroEarly.cpp

@@ -203,7 +203,7 @@ void Lowerer::lowerEarlyIntrinsics(Function &F) {
           if (CII->getInfo().isPreSplit()) {
             assert(F.isPresplitCoroutine() &&
                    "The frontend uses Swtich-Resumed ABI should emit "
-                   "\"coroutine.presplit\" attribute for the coroutine.");
+                   "\"presplitcoroutine\" attribute for the coroutine.");
             setCannotDuplicate(CII);
             CII->setCoroutineSelf();
             CoroId = cast<CoroIdInst>(&I);

mlir/lib/Dialect/Async/Transforms/AsyncToAsyncRuntime.cpp

@@ -242,7 +242,7 @@ static CoroMachinery setupCoroMachinery(func::FuncOp func) {
   // continuations, and will conditionally branch to cleanup or suspend blocks.
 
   // The switch-resumed API based coroutine should be marked with
-  // coroutine.presplit attribute to mark the function as a coroutine.
+  // presplitcoroutine attribute to mark the function as a coroutine.
   func->setAttr("passthrough", builder.getArrayAttr(
                                    StringAttr::get(ctx, "presplitcoroutine")));