Fix the bug from unit tests.

********************
Failed Tests (2):
  LLVM-Unit :: Transforms/Vectorize/./VectorizeTests/21/51
  LLVM-Unit :: Transforms/Vectorize/./VectorizeTests/26/51

Author: Mel-Chen

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -2233,7 +2233,7 @@ class VPReductionEVLRecipe : public VPReductionRecipe {
   VPReductionEVLRecipe(VPReductionRecipe *R, VPValue *EVL, VPValue *CondOp)
       : VPReductionRecipe(
             VPDef::VPReductionEVLSC, R->getRecurrenceDescriptor(),
-            R->getUnderlyingInstr(),
+            cast_or_null<Instruction>(R->getUnderlyingValue()),
             ArrayRef<VPValue *>({R->getChainOp(), R->getVecOp(), EVL}), CondOp,
             R->isOrdered()) {}