commit-graph: stop using optname()

Stop using optname() in builtin/commit-graph.c to emit an error with
the --max-new-filters option. This changes code added in 809e0327f5
(builtin/commit-graph.c: introduce '--max-new-filters=<n>',
2020-09-18).

See 9440b831ad (parse-options: replace opterror() with optname(),
2018-11-10) for why using optname() like this is considered bad,
i.e. it's assembling human-readable output piecemeal, and the "option
`X'" at the start can't be translated.

It didn't matter in this case, but this code was also buggy in its use
of "opt->flags" to optname(), that function expects flags, but not
*those* flags.

Let's pass "max-new-filters" to the new error because the option name
isn't translatable, and because we can re-use a translation added in
f7e68a0878 (parse-options: check empty value in OPT_INTEGER and
OPT_ABBREV, 2019-05-29).

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

builtin/commit-graph.c

@@ -172,8 +172,8 @@ static int write_option_max_new_filters(const struct option *opt,
 		const char *s;
 		*to = strtol(arg, (char **)&s, 10);
 		if (*s)
-			return error(_("%s expects a numerical value"),
+			return error(_("option `%s' expects a numerical value"),
-				     optname(opt, opt->flags));
+				     "max-new-filters");
 	}
 	return 0;
 }