dm: restore synchronous close of device mapper block device

'dmsetup remove' and 'dmsetup remove_all' require synchronous bdev
release. Otherwise dm_lock_for_deletion() may return -EBUSY if the open
count is > 0, because the open count is dropped in dm_blk_close()
which occurs after fput() completes.

So if dm_blk_close() is delayed because of asynchronous fput(), this
device mapper device is skipped during remove, which is a regression.

Fix the issue by using __fput_sync().

Also, DM device removal has long supported being made asynchronous by
setting the DMF_DEFERRED_REMOVE flag on the DM device. So leverage
using async fput() in close_table_device() if DMF_DEFERRED_REMOVE flag
is set.

Reported-by: Zhong Changhui <czhong@redhat.com>
Fixes: a28d893e

 ("md: port block device access to file")
Suggested-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
[snitzer: editted commit header, use fput() if DMF_DEFERRED_REMOVE set]
Signed-off-by: Mike Snitzer <snitzer@kernel.org>