xfs: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style in header files
related to XFS File System support. For C header files
Documentation/process/license-rules.rst mandates C-like comments.
(opposed to C source files where C++ style should be used).

Changes made by using a script provided by Joe Perches here:
https://lkml.org/lkml/2019/2/7/46.
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Nishad Kamdar <nishadkamdar@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/kmem.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000-2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_ag_resv.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Copyright (C) 2016 Oracle.  All Rights Reserved.
  * Author: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/libxfs/xfs_alloc.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_alloc_btree.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000,2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_attr.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000,2002-2003,2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_attr_leaf.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000,2002-2003,2005 Silicon Graphics, Inc.
  * Copyright (c) 2013 Red Hat, Inc.

fs/xfs/libxfs/xfs_attr_remote.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2013 Red Hat, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_attr_sf.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000,2002,2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_bit.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000,2002,2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_bmap.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000-2006 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_bmap_btree.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000,2002-2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_btree.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000-2001,2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_da_btree.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000,2002,2005 Silicon Graphics, Inc.
  * Copyright (c) 2013 Red Hat, Inc.

fs/xfs/libxfs/xfs_da_format.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000-2001,2005 Silicon Graphics, Inc.
  * Copyright (c) 2013 Red Hat, Inc.

fs/xfs/libxfs/xfs_defer.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Copyright (C) 2016 Oracle.  All Rights Reserved.
  * Author: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/libxfs/xfs_dir2.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000-2001,2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_dir2_priv.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000-2001,2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_errortag.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
  * Copyright (C) 2017 Oracle.

fs/xfs/libxfs/xfs_format.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (c) 2000-2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_fs.h

-// SPDX-License-Identifier: LGPL-2.1
+/* SPDX-License-Identifier: LGPL-2.1 */
 /*
  * Copyright (c) 1995-2005 Silicon Graphics, Inc.
  * All Rights Reserved.

fs/xfs/libxfs/xfs_health.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Copyright (C) 2019 Oracle.  All Rights Reserved.
  * Author: Darrick J. Wong <darrick.wong@oracle.com>