submodule-config: use hashmap_iter_first()

The hashmap API provides hashmap_iter_first() helper for initialion
and getting the first entry of a hashmap. Let's use it instead of
doing initialization manually and then get the first entry.

There are no functional changes, just cleanup.

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Reviewed-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

submodule-config.c

@@ -392,8 +392,7 @@ static const struct submodule *config_from(struct submodule_cache *cache,
 		struct hashmap_iter iter;
 		struct submodule_entry *entry;
 
-		hashmap_iter_init(&cache->for_name, &iter);
-		entry = hashmap_iter_next(&iter);
+		entry = hashmap_iter_first(&cache->for_name, &iter);
 		if (!entry)
 			return NULL;
 		return entry->config;