drivers: isdn: eicon: xdi_msg.h: Fix typo in #ifndef

Test for definedness of the macro which is actually defined (the
change is hard to see: it is s/SSS/SSA/).
Signed-off-by: NRasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/isdn/hardware/eicon/xdi_msg.h

 /* $Id: xdi_msg.h,v 1.1.2.2 2001/02/16 08:40:36 armin Exp $ */
 
-#ifndef __DIVA_XDI_UM_CFG_MESSSGE_H__
+#ifndef __DIVA_XDI_UM_CFG_MESSAGE_H__
 #define __DIVA_XDI_UM_CFG_MESSAGE_H__
 
 /*