dm: don't report warning when doing deferred remove

dm: don't report warning when doing deferred remove

If dm_hash_remove_all was called from dm_deferred_remove, it would write
a warning "remove_all left %d open device(s)" if there are some other
devices active.

The warning is bogus, so let's disable it in this case.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 2c140a246dc0 ("dm: allow remove to be deferred")