[ValueLattice] Fix typo in condition (NFC)

Fix typo pointed out by Roman Divacky.

There should be no functional change, as the rest of the code will
return nullptr for undef anyway. The condition is just there for
clarity.

Author: nikic

llvm/lib/Analysis/ValueLattice.cpp

@@ -20,7 +20,7 @@ ValueLatticeElement::getCompare(CmpInst::Predicate Pred, Type *Ty,
 
   // TODO: Can be made more precise, but always returning undef would be
   // incorrect.
-  if (isUndef() || isUndef())
+  if (isUndef() || Other.isUndef())
     return nullptr;
 
   if (isConstant() && Other.isConstant())