Lock dq_dqb_lock around dquot_decr_inodes()
Signed-off-by: NKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Fixes: 7b9ca4c6 ("quota: Reduce contention on dq_data_lock")
Signed-off-by: NJan Kara <jack@suse.cz>