remote: fix remote set-url usage

Bad copy-paste.

Otherwise the help text for "git remote set-url --help" would show help
for "git remote update" subcommand.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-remote.c

@@ -1286,7 +1286,7 @@ static int set_url(int argc, const char **argv)
 			    "delete URLs"),
 		OPT_END()
 	};
-	argc = parse_options(argc, argv, NULL, options, builtin_remote_update_usage,
+	argc = parse_options(argc, argv, NULL, options, builtin_remote_seturl_usage,
 			     PARSE_OPT_KEEP_ARGV0);
 
 	if (add_mode && delete_mode)