quota: add new helper dquot_active()

Add new helper function dquot_active() to make the code more concise.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20230630110822.3881712-4-libaokun1@huawei.com>