nvmet: zns: Do not reference the gendisk conv_zones_bitmap

nvmet: zns: Do not reference the gendisk conv_zones_bitmap

The gendisk conventional zone bitmap is going away. So to check for the
presence of conventional zones on a zoned target device, always use
report zones.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Tested-by: Hans Holmberg <hans.holmberg@wdc.com>
Tested-by: Dennis Maisenbacher <dennis.maisenbacher@wdc.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20240408014128.205141-19-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>