NFC: Add an explicit return for safety and consistency

This case implicitly falls-through, which is fine now as it's at the end of the
function, but it seems like an accident waiting to happen.

llvm-svn: 365210

clang/lib/CodeGen/CGDecl.cpp

@@ -153,6 +153,8 @@ void CodeGenFunction::EmitDecl(const Decl &D) {
 
     if (Ty->isVariablyModifiedType())
       EmitVariablyModifiedType(Ty);
+
+    return;
   }
   }
 }