os/bluestore: Fix deferred writes corrupting RocksDB

os/bluestore: Fix deferred writes corrupting RocksDB

Deferred writes can sometimes update regions that are no longer mapped to any object.
This cannot happen when BlueStore is running, as blobs are being held,
and allocations are not released until deferred op is executed.
However in case of restart allocations that deferred is targetting are already freed.
Deferred replay is done on BlueStore bootup, before any new object can be allocated,
so no collision with object is possible.
But BlueFS can allocate space from block with deferred ops still pending.

Fixes: https://tracker.ceph.com/issues/54547
Signed-off-by: Adam Kupczyk <akupczyk@redhat.com>