mxs: Replace i.MX233 by i.MX23 on copyright header

All other header are going to use i.MX23 so we change this for
consistency.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>

arch/arm/include/asm/arch-mxs/sys_proto.h

@@ -1,5 +1,5 @@
 /*
- * Freescale i.MX233/i.MX28 specific functions
+ * Freescale i.MX23/i.MX28 specific functions
  *
  * Copyright (C) 2011 Marek Vasut <marek.vasut@gmail.com>
  * on behalf of DENX Software Engineering GmbH