[VPlan] Update stale comment (NFC).

Update comment to reflect current code, which also allows for
VPScalarIVStepsRecipes to be uniform.

Suggested by @ayal during review of D136068, thanks!

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -9873,7 +9873,7 @@ Value *VPTransformState::get(VPValue *Def, unsigned Part) {
   unsigned LastLane = IsUniform ? 0 : VF.getKnownMinValue() - 1;
   // Check if there is a scalar value for the selected lane.
   if (!hasScalarValue(Def, {Part, LastLane})) {
-    // At the moment, VPWidenIntOrFpInductionRecipes can also be uniform.
+    // At the moment, VPWidenIntOrFpInductionRecipes and VPScalarIVStepsRecipes can also be uniform.
     assert((isa<VPWidenIntOrFpInductionRecipe>(Def->getDefiningRecipe()) ||
             isa<VPScalarIVStepsRecipe>(Def->getDefiningRecipe())) &&
            "unexpected recipe found to be invariant");