Convert device mapper to use bdev_open_by_dev() and pass the handle
around.

CC: Alasdair Kergon <agk@redhat.com>
CC: Mike Snitzer <snitzer@kernel.org>
CC: dm-devel@redhat.com
Acked-by: Christoph Hellwig <hch@lst.de>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230927093442.25915-10-jack@suse.czSigned-off-by: Christian Brauner <brauner@kernel.org>