Codegen - silence static analyzer getAs<> null dereference warnings. NFCI.

The static analyzer is warning about potential null dereferences, but in these cases we should be able to use castAs<> directly and if not assert will fire for us.

llvm-svn: 373918
diff --git a/clang/lib/CodeGen/CGObjCGNU.cpp b/clang/lib/CodeGen/CGObjCGNU.cpp
index c21f257..d2c089d 100644
--- a/clang/lib/CodeGen/CGObjCGNU.cpp
+++ b/clang/lib/CodeGen/CGObjCGNU.cpp
@@ -4040,7 +4040,7 @@
                                        const ObjCIvarDecl *Ivar,
                                        unsigned CVRQualifiers) {
   const ObjCInterfaceDecl *ID =
-    ObjectTy->getAs<ObjCObjectType>()->getInterface();
+    ObjectTy->castAs<ObjCObjectType>()->getInterface();
   return EmitValueForIvarAtOffset(CGF, ID, BaseValue, Ivar, CVRQualifiers,
                                   EmitIvarOffset(CGF, ID, Ivar));
 }