md/md-bitmap: Add missing destroy_work_on_stack()

This commit add missed destroy_work_on_stack() operations for
unplug_work.work in bitmap_unplug_async().

Fixes: a022325a ("md/md-bitmap: add a new helper to unplug bitmap asynchrously")
Cc: stable@vger.kernel.org
Signed-off-by: Yuan Can <yuancan@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20241105130105.127336-1-yuancan@huawei.com


Signed-off-by: Song Liu <song@kernel.org>