spi: bcm53xx: (re)license code to the GPL v2

My intention was to release this code under GPL v2 license. For some
reason my initial commit 0fc6a323e191 ("spi: bcm53xx: driver for SPI
controller on Broadcom bcma SoC") totally missed licensing info.
MODULE_LICENSE was later added by Axel specifying "GNU Public License
v2 or later".

This patch clarifies situation by adding a proper header (with Copyright
line) and adjusting MODULE_LICENSE. It should be acked by every driver
contributor.

Signed-off-by: Rafał Miłecki <[e-mail]>
Acked-by: Nicholas Mc Guire <[e-mail]>
Reviewed-by: Jingoo Han <[e-mail]>
Acked-by: Jingoo Han <[e-mail]>
Acked-by: Joe Perches <[e-mail]>
Acked-by: Axel Lin <[e-mail]>
Acked-by: Vaishali Thakkar <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-bcm53xx.c

···
+/*
+ * Copyright (C) 2014-2016 Rafał Miłecki <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
 #define pr_fmt(fmt)		KBUILD_MODNAME ": " fmt
 
 #include <linux/kernel.h>
···
 
 MODULE_DESCRIPTION("Broadcom BCM53xx SPI Controller driver");
 MODULE_AUTHOR("Rafał Miłecki <[e-mail]>");
-MODULE_LICENSE("GPL");
+MODULE_LICENSE("GPL v2");