tblgen: Use semantically correct RTTI functions.

Also, some minor cleanup.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165647 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/SetTheory.cpp b/utils/TableGen/SetTheory.cpp
index dcc8871..5b760e7 100644
--- a/utils/TableGen/SetTheory.cpp
+++ b/utils/TableGen/SetTheory.cpp
@@ -193,7 +193,7 @@
       throw "To out of range";
 
     RecordKeeper &Records =
-      dyn_cast<DefInit>(Expr->getOperator())->getDef()->getRecords();
+      cast<DefInit>(Expr->getOperator())->getDef()->getRecords();
 
     Step *= From <= To ? 1 : -1;
     while (true) {