FROMLIST: dm-zone: use generic helpers to calculate offset from zone start

Use the bdev_offset_from_zone_start() helper function to calculate
the offset from zone start instead of using power of 2 based
calculation.

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
Bug: 197782466
Bug: 269471019
Link: https://lore.kernel.org/linux-block/20220923173618.6899-10-p.raghav@samsung.com/


Change-Id: If04c016235c87e23b2b544f947ae8bdfc3df4c48
Signed-off-by: Bart Van Assche <bvanassche@google.com>