Blackfin: drop bfin #undef in linker script

Now that the linker script is preprocessed with -ansi, there is no need to
manually undef the bfin define.
Signed-off-by: NMike Frysinger <vapier@gentoo.org>

lib_blackfin/u-boot.lds.S

 /*
  * U-boot - u-boot.lds.S
  *
- * Copyright (c) 2005-2008 Analog Device Inc.
+ * Copyright (c) 2005-2010 Analog Device Inc.
  *
  * (C) Copyright 2000-2004
  * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
@@ -29,7 +29,6 @@
 #include <asm/blackfin.h>
 #undef ALIGN
 #undef ENTRY
-#undef bfin
 
 #ifndef LDS_BOARD_TEXT
 # define LDS_BOARD_TEXT