fix format string (inspired by issue #4945)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@6415 65c4cc65-6c06-0410-ace0-fbb531ad65f3

cli.c

@@ -1340,7 +1340,7 @@ int ast_cli_command(int fd, char *s)
 			if (e) {
 				switch(e->handler(fd, x, argv)) {
 				case RESULT_SHOWUSAGE:
-					ast_cli(fd, e->usage);
+					ast_cli(fd, "%s", e->usage);
 					break;
 				}
 			} else