Fix warning caused by ReductionTreePass class

[msifontes]

Summary

Explicitly declare ReductionTreeBase base class in ReductionTreePass copy constructor.

mlir/include/mlir/Reducer/ReductionTreePass.h

 /// generated reduced variants.
 template <typename Reducer, TraversalMode mode>
 class ReductionTreePass
     : public ReductionTreeBase<ReductionTreePass<Reducer, mode>> {
 public:
   ReductionTreePass(const Tester *test) : test(test) {}
 
   ReductionTreePass(const ReductionTreePass &pass)
-      : root(new ReductionNode(pass.root->getModule().clone(), nullptr)),
+      : ReductionTreeBase<ReductionTreePass<Reducer, mode>>(pass),
+        root(new ReductionNode(pass.root->getModule().clone(), nullptr)),
         test(pass.test) {}
 
   /// Runs the pass instance in the pass pipeline.
   void runOnOperation() override {
     ModuleOp module = this->getOperation();
     this->root = std::make_unique<ReductionNode>(module, nullptr);
     ReductionNode *reduced;