ctype: constify lookup table

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/include/linux/ctype.h b/include/linux/ctype.h
index afa3639..6dec944 100644
--- a/include/linux/ctype.h
+++ b/include/linux/ctype.h
@@ -15,7 +15,7 @@
 #define _X	0x40	/* hex digit */
 #define _SP	0x80	/* hard space (0x20) */
 
-extern unsigned char _ctype[];
+extern const unsigned char _ctype[];
 
 #define __ismask(x) (_ctype[(int)(unsigned char)(x)])