btrfs: replace GPL boilerplate by SPDX -- headers

Remove GPL boilerplate text (long, short, one-line) and keep the rest,
ie. personal, company or original source copyright statements. Add the
SPDX header.

Unify the include protection macros to match the file names.

Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ref-verify.h

@@ -1,22 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2014 Facebook.  All rights reserved.
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public
- * License v2 as published by the Free Software Foundation.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * General Public License for more details.
- *
- * You should have received a copy of the GNU General Public
- * License along with this program; if not, write to the
- * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
- * Boston, MA 021110-1307, USA.
  */
-#ifndef __REF_VERIFY__
-#define __REF_VERIFY__
+
+#ifndef BTRFS_REF_VERIFY_H
+#define BTRFS_REF_VERIFY_H
 
 #ifdef CONFIG_BTRFS_FS_REF_VERIFY
 int btrfs_build_ref_tree(struct btrfs_fs_info *fs_info);
@@ -59,4 +47,5 @@ static inline void btrfs_init_ref_verify(struct btrfs_fs_info *fs_info)
 }
 
 #endif /* CONFIG_BTRFS_FS_REF_VERIFY */
-#endif /* _REF_VERIFY__ */
+
+#endif