dm-zoned: remove the ->name field in struct dmz_dev

Just use the %pg format specifier to print the block device name
directly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>