cbfstool: index is replaced by strchr.

From index(3):
CONFORMING TO 4.3BSD; marked as LEGACY in POSIX.1-2001. POSIX.1-2008
removes the specifications of index() and rindex(), recommending
strchr(3) and strrchr(3) instead.

Change-Id: I3899b9ca9196dbbf2d147a38dacd7e742a3873fe
Signed-off-by: Zheng Bao <zheng.bao@amd.com>
Signed-off-by: zbao <fishbaozi@gmail.com>
Reviewed-on: http://review.coreboot.org/2112
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

util/cbfstool/cbfstool.c

@@ -563,7 +563,7 @@ int main(int argc, char **argv)
 				break;
 
 			/* filter out illegal long options */
-			if (index(commands[i].optstring, c) == NULL) {
+			if (strchr(commands[i].optstring, c) == NULL) {
 				/* TODO maybe print actual long option instead */
 				printf("%s: invalid option -- '%c'\n",
 					argv[0], c);