[SCEV] Use ListSeparator (NFC)

Author: kazutakahirata

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -321,12 +321,9 @@ void SCEV::print(raw_ostream &OS) const {
       llvm_unreachable("There are no other nary expression types.");
     }
     OS << "(";
-    for (SCEVNAryExpr::op_iterator I = NAry->op_begin(), E = NAry->op_end();
-         I != E; ++I) {
-      OS << **I;
-      if (std::next(I) != E)
-        OS << OpStr;
-    }
+    ListSeparator LS(OpStr);
+    for (const SCEV *Op : NAry->operands())
+      OS << LS << *Op;
     OS << ")";
     switch (NAry->getSCEVType()) {
     case scAddExpr: