patman: Fix unit tests for SPDX

The format of this line has changed. Update the patman test to suit.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Alex Kiernan <alex.kiernan@gmail.com>

tools/patman/test.py

@@ -148,7 +148,7 @@ index 0000000..2234c87
 --- /dev/null
 +++ b/common/bootstage.c
 @@ -0,0 +1,37 @@
-+/* SPDX-License-Identifier: GPL-2.0+ */
++// SPDX-License-Identifier: GPL-2.0+
 +/*
 + * Copyright (c) 2011, Google Inc. All rights reserved.
 + *