[SandboxVec][NullPass][NFC] Add missing banner comment at top of file

Author: vporpo

llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/Passes/NullPass.h

@@ -1,3 +1,14 @@
+//===- NullPass.h -----------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// A null region pass that does nothing. Used for testing.
+//
+
 #ifndef LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_PASSES_NULLPASS_H
 #define LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_PASSES_NULLPASS_H