Fix warning on qualified typedef with 'unused' attribute, from Jason Haslam!

llvm-svn: 163874
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 92780d9..7903ed0 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -1264,7 +1264,7 @@
     QualType Ty = VD->getType();
 
     // Only look at the outermost level of typedef.
-    if (const TypedefType *TT = dyn_cast<TypedefType>(Ty)) {
+    if (const TypedefType *TT = Ty->getAs<TypedefType>()) {
       if (TT->getDecl()->hasAttr<UnusedAttr>())
         return false;
     }