block: refactor blkdev_report_zones() code

block: refactor blkdev_report_zones() code

In preparation for implementing cached report zone, split the main part
of the code of blkdev_report_zones() into the helper function
blkdev_do_report_zones(), with this new helper taking as argument a
struct blk_report_zones_args pointer instead of a report callback
function and its private argument.

No functional changes.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>