mark unused read_tree_recursive() callback parameters

We pass a callback to read_tree_recursive(), but not every callback
needs every parameter. Let's mark the unused ones to satisfy
-Wunused-parameter.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -125,7 +125,7 @@ static int post_checkout_hook(struct commit *old_commit, struct commit *new_comm
 }
 
 static int update_some(const struct object_id *oid, struct strbuf *base,
-		const char *pathname, unsigned mode, void *context)
+		       const char *pathname, unsigned mode, void *UNUSED(context))
 {
 	int len;
 	struct cache_entry *ce;