[LV] Use getMask() when printing recipe [NFCI]

[gilr]

Summary

Use dedicated API for getting the mask instead of duplicating it.

[fhahn]

LGTM

[gilr]

In D71964#1798095, @fhahn wrote:

LGTM

Thanks @fhahn !

llvm/lib/Transforms/Vectorize/VPlan.h

 
   /// Return the mask used by this recipe. Note that a full mask is represented
   /// by a nullptr.
-  VPValue *getMask() {
+  VPValue *getMask() const {
     // Mask is the last operand.
     return User ? User->getOperand(User->getNumOperands() - 1) : nullptr;
   }

llvm/lib/Transforms/Vectorize/VPlan.cpp

 void VPWidenMemoryInstructionRecipe::print(raw_ostream &O,
                                            const Twine &Indent) const {
   O << " +\n" << Indent << "\"WIDEN " << VPlanIngredient(&Instr);
-  if (User) {
+  VPValue *Mask = getMask();
+  if (Mask) {
     O << ", ";
-    User->getOperand(0)->printAsOperand(O);
+    Mask->printAsOperand(O);
   }
   O << "\\l\"";
 }