completion: use __gitcomp_builtin in _git_add

The new completable options are

--all
--ignore-missing
--ignore-removal
--renormalize
--verbose

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -1153,10 +1153,7 @@ _git_add ()
 {
 	case "$cur" in
 	--*)
-		__gitcomp "
-			--interactive --refresh --patch --update --dry-run
-			--ignore-errors --intent-to-add --force --edit --chmod=
-			"
+		__gitcomp_builtin add
 		return
 	esac