[VPlan] Make sure vector trip count is ready for prepareToExecute (NFC)

Split off from llvm#112145. This
ensures that getOrCreateVectorTripCount creates the trip count as needed
when induction resume value creation is moved to VPlan and no longer
creates the vector trip count early.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -7827,8 +7827,9 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   //===------------------------------------------------===//
 
   // 2. Copy and widen instructions from the old loop into the new loop.
-  BestVPlan.prepareToExecute(ILV.getTripCount(),
-                             ILV.getOrCreateVectorTripCount(nullptr), State);
+  BestVPlan.prepareToExecute(
+      ILV.getTripCount(),
+      ILV.getOrCreateVectorTripCount(ILV.LoopVectorPreHeader), State);
 
   BestVPlan.execute(&State);