dm: retun the clone bio from alloc_tio

Return the clone bio embedded into the tio as that is what the callers
actually want.  Similar for the free side.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Link: https://lore.kernel.org/r/20220202160109.108149-8-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>