Instead of open coding, use the min() macro to calculate a report zones
reply buffer length in sd_zbc_check_zone_size() and the round_up() macro
for calculating the number of zones in sd_zbc_setup().

No functional change is introduced by this patch.
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>