mtd: nand: tango: Add standard legalese header

Provide proper copyright notice and license information.
Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/tango_nand.c

+/*
+ * Copyright (C) 2016 Sigma Designs
+ *
+ * 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.
+ */
+
 #include <linux/io.h>
 #include <linux/of.h>
 #include <linux/clk.h>