Fix spelling of 'platform' in comments and doc

Replace platfrom -> platform.

This is a frequent spelling bug.

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/mtd/maps/plat-ram.c b/drivers/mtd/maps/plat-ram.c
index dafb919..76a76be 100644
--- a/drivers/mtd/maps/plat-ram.c
+++ b/drivers/mtd/maps/plat-ram.c
@@ -4,7 +4,7 @@
  *	http://www.simtec.co.uk/products/SWLINUX/
  *	Ben Dooks <ben@simtec.co.uk>
  *
- * Generic platfrom device based RAM map
+ * Generic platform device based RAM map
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by