[VPlan] Use isa<> instead getVPRecipeID in getFirstNonPhi (NFC).

As per the comment in VPRecipeBase, clients should not rely on
getVPRecipeID, as it may change in the future. It should only be used in
classof implementations. Use isa instead in getFirstNonPhi.

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -213,11 +213,10 @@ void VPBlockBase::deleteCFG(VPBlockBase *Entry) {
 
 VPBasicBlock::iterator VPBasicBlock::getFirstNonPhi() {
   iterator It = begin();
-  while (It != end() &&
-         (It->getVPRecipeID() == VPRecipeBase::VPWidenPHISC ||
-          It->getVPRecipeID() == VPRecipeBase::VPWidenIntOrFpInductionSC ||
-          It->getVPRecipeID() == VPRecipeBase::VPPredInstPHISC ||
-          It->getVPRecipeID() == VPRecipeBase::VPWidenCanonicalIVSC))
+  while (It != end() && (isa<VPWidenPHIRecipe>(&*It) ||
+                         isa<VPWidenIntOrFpInductionRecipe>(&*It) ||
+                         isa<VPPredInstPHIRecipe>(&*It) ||
+                         isa<VPWidenCanonicalIVRecipe>(&*It)))
     It++;
   return It;
 }