md: wake up 'resync_wait' at last in md_reap_sync_thread()

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6OMCC


CVE: NA

--------------------------------

We just replace md_reap_sync_thread() with wait_event(resync_wait, ...)
from action_store(), this patch just make sure action_store() will still
wait for everything to be done in md_reap_sync_thread().

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>