Remove unnecessary null check. NFC.

Since both places which set this variable do so with dyn_cast, and not
dyn_cast_or_null, its impossible to get a nullptr here, so we can remove
the check.

llvm-svn: 243167

llvm/lib/Transforms/Scalar/LoopInterchange.cpp

@@ -817,9 +817,6 @@ bool LoopInterchangeLegality::currentLimitations() {
     InnerIndexVarInc =
         dyn_cast<Instruction>(InnerInductionVar->getIncomingValue(0));
 
-  if (!InnerIndexVarInc)
-    return true;
-
   // Since we split the inner loop latch on this induction variable. Make sure
   // we do not have any instruction between the induction variable and branch
   // instruction.