f2fs: add SPDX license identifiers

Remove the verbose license text from f2fs files and replace them with
SPDX tags.  This does not change the license of any of the code.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
index ebe649d..d3c4021 100644
--- a/fs/f2fs/debug.c
+++ b/fs/f2fs/debug.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * f2fs debugging statistics
  *
@@ -5,10 +6,6 @@
  *             http://www.samsung.com/
  * Copyright (c) 2012 Linux Foundation
  * Copyright (c) 2012 Greg Kroah-Hartman <gregkh@linuxfoundation.org>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
  */
 
 #include <linux/fs.h>