regulator: lochnagar: Use a consisent comment style for SPDX header

Update the rest of the comment at the start of the file to also use C++
style comments to match the required style of the SPDX header.
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/lochnagar-regulator.c

 // SPDX-License-Identifier: GPL-2.0
-/*
- * Lochnagar regulator driver
- *
- * Copyright (c) 2017-2018 Cirrus Logic, Inc. and
- *                         Cirrus Logic International Semiconductor Ltd.
- *
- * Author: Charles Keepax <ckeepax@opensource.cirrus.com>
- */
+//
+// Lochnagar regulator driver
+//
+// Copyright (c) 2017-2018 Cirrus Logic, Inc. and
+//                         Cirrus Logic International Semiconductor Ltd.
+//
+// Author: Charles Keepax <ckeepax@opensource.cirrus.com>
 
 #include <linux/bitops.h>
 #include <linux/device.h>