completion: use __gitcomp_builtin in _git_worktree

The new completable options for "worktree add" are:

--checkout
--guess-remote
--lock
--track

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 4d3422f..76dc6b8 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -367,7 +367,7 @@ static int add(int ac, const char **av, const char *prefix)
 	struct option options[] = {
 		OPT__FORCE(&opts.force,
 			   N_("checkout <branch> even if already checked out in other worktree"),
-			   0),
+			   PARSE_OPT_NOCOMPLETE),
 		OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
 			   N_("create a new branch")),
 		OPT_STRING('B', NULL, &new_branch_force, N_("branch"),