zbd: introduce zbd_zone_align_file_sizes() helper

zbd: introduce zbd_zone_align_file_sizes() helper

Move the code for the innermost loop of the function zbd_verify_sizes()
to the new helper function zbd_zone_align_file_sizes(). This helper
avoids large indentation of the code in zbd_verify_sizes() and makes
the code easier to read.

No functional changes.

Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Niklas Cassel <niklas.cassel@wdc.com>
Link: https://lore.kernel.org/r/20211214012413.464798-6-damien.lemoal@opensource.wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>