nvme-loop: convert to SPDX identifiers

Update license to use SPDX-License-Identifier instead of verbose license
text.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

drivers/nvme/target/loop.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * NVMe over Fabrics loopback device.
  * Copyright (c) 2015-2016 HGST, a Western Digital Company.
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms and conditions of the GNU General Public License,
- * version 2, as published by the Free Software Foundation.
- *
- * This program is distributed in the hope 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.
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 #include <linux/scatterlist.h>