usage.c API users: use die_message() for error() + exit 128

Continue the migration of code that printed a message and exited with
128. In this case the caller used "error()", so we'll be changing the
output from "error: " to "fatal: ". This change is intentional and
desired.

This code is dying, so it should emit "fatal", the only reason it
didn't do so was because before the existence of "die_message()" it
would have needed to craft its own "fatal: " message.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: avar

builtin/notes.c

@@ -201,11 +201,12 @@ static void prepare_note_data(const struct object_id *object, struct note_data *
 static void write_note_data(struct note_data *d, struct object_id *oid)
 {
 	if (write_object_file(d->buf.buf, d->buf.len, blob_type, oid)) {
-		error(_("unable to write note object"));
+		int status = die_message(_("unable to write note object"));
+
 		if (d->edit_path)
-			error(_("the note contents have been left in %s"),
-				d->edit_path);
-		exit(128);
+			die_message(_("the note contents have been left in %s"),
+				    d->edit_path);
+		exit(status);
 	}
 }