block: use lcm_not_zero() when stacking chunk_sectors

block: use lcm_not_zero() when stacking chunk_sectors

Like 'io_opt', blk_stack_limits() should stack 'chunk_sectors' using
lcm_not_zero() rather than min_not_zero() -- otherwise the final
'chunk_sectors' could result in sub-optimal alignment of IO to
component devices in the IO stack.

Also, if 'chunk_sectors' isn't a multiple of 'physical_block_size'
then it is a bug in the driver and the device should be flagged as
'misaligned'.

Reviewed-by: Ming Lei <[email protected]>
Reviewed-by: Martin K. Petersen <[email protected]>
Signed-off-by: Mike Snitzer <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>