name-rev: avoid unnecessary cast in name_ref()

Casting a 'struct object' to 'struct commit' is unnecessary there,
because it's already available in the local 'commit' variable.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/name-rev.c

@@ -272,7 +272,7 @@ static int name_ref(const char *path, const struct object_id *oid, int flags, vo
 		int from_tag = starts_with(path, "refs/tags/");
 
 		if (taggerdate == TIME_MAX)
-			taggerdate = ((struct commit *)o)->date;
+			taggerdate = commit->date;
 		path = name_ref_abbrev(path, can_abbreviate_output);
 		name_rev(commit, xstrdup(path), taggerdate, 0, 0,
 			 from_tag, deref);