[CIR] Fix mlir::ValueRange init from ArrayRef warning (#146577)

Fix initalizing ValueRange with ArrayRef
`ValueRange(ArrayRef<Value>(std::forward<Arg>(arg))) {}` warning

clang/include/clang/CIR/Dialect/IR/CIROps.td

@@ -489,7 +489,7 @@ def ReturnOp : CIR_Op<"return", [ParentOneOf<["FuncOp", "ScopeOp", "IfOp",
 
   // Allow building a ReturnOp with no return operand.
   let builders = [
-    OpBuilder<(ins), [{ build($_builder, $_state, std::nullopt); }]>
+    OpBuilder<(ins), [{ build($_builder, $_state, {}); }]>
   ];
 
   // Provide extra utility definitions on the c++ operation class definition.