extcon: usbc-cros-ec: Switch to SPDX identifier.

Adopt the SPDX license identifier headers to ease license compliance
management.
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

drivers/extcon/extcon-usbc-cros-ec.c

-/**
- * drivers/extcon/extcon-usbc-cros-ec - ChromeOS Embedded Controller extcon
- *
- * Copyright (C) 2017 Google, Inc
- * Author: Benson Leung <bleung@chromium.org>
- *
- * This software is licensed under the terms of the GNU General Public
- * License version 2, as published by the Free Software Foundation, and
- * may be copied, distributed, and modified under those terms.
- *
- * 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.
- */
+// SPDX-License-Identifier: GPL-2.0
+// ChromeOS Embedded Controller extcon
+//
+// Copyright (C) 2017 Google, Inc.
+// Author: Benson Leung <bleung@chromium.org>
 
 #include <linux/extcon-provider.h>
 #include <linux/kernel.h>