[LoopInterchange] Address nit

Author: artagnon

llvm/lib/Transforms/Scalar/LoopInterchange.cpp

@@ -551,10 +551,10 @@ struct LoopInterchange {
     //
     // For the old pass manager CacheCost would be null.
     DenseMap<const Loop *, unsigned> CostMap;
-    if (CC)
+    if (CC != nullptr) {
       for (const auto &[Idx, Cost] : enumerate(CC->getLoopCosts()))
         CostMap[Cost.first] = Idx;
-
+    }
     // We try to achieve the globally optimal memory access for the loopnest,
     // and do interchange based on a bubble-sort fasion. We start from
     // the innermost loop, move it outwards to the best possible position