block: make sure writesame bio is aligned with logical block size

block: make sure writesame bio is aligned with logical block size

Obviously the created writesame bio has to be aligned with logical block
size, and use bio_allowed_max_sectors() to retrieve this number.

Cc: [email protected]
Cc: Mike Snitzer <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Xiao Ni <[email protected]>
Cc: Mariusz Dabrowski <[email protected]>
Fixes: b49a0871be31a745b2ef ("block: remove split code in blkdev_issue_{discard,write_same}")
Tested-by: Rui Salvaterra <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>