[VPlan] Fold if into return in prepareToExecute assertion (NFC).

Independent simplification suggested in D157194.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -758,12 +758,10 @@ void VPlan::prepareToExecute(Value *TripCountV, Value *VectorTripCountV,
     auto *IV = getCanonicalIV();
     assert(all_of(IV->users(),
                   [](const VPUser *U) {
-                    if (isa<VPScalarIVStepsRecipe>(U) ||
-                        isa<VPDerivedIVRecipe>(U))
-                      return true;
-                    auto *VPI = cast<VPInstruction>(U);
-                    return VPI->getOpcode() ==
-                           VPInstruction::CanonicalIVIncrement;
+                    return isa<VPScalarIVStepsRecipe>(U) ||
+                           isa<VPDerivedIVRecipe>(U) ||
+                           cast<VPInstruction>(U)->getOpcode() ==
+                               VPInstruction::CanonicalIVIncrement;
                   }) &&
            "the canonical IV should only be used by its increment or "
            "ScalarIVSteps when resetting the start value");