block: Fix incorrect reporting of partition alignment

block: Fix incorrect reporting of partition alignment

commit 81744ee44ab2845c16ffd7d6f762f7b4a49a4750 upstream

queue_sector_alignment_offset returned the wrong value which caused
partitions to report an incorrect alignment_offset. Since offset
calculation is needed several places it has been split into a separate
helper function.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Tested-by: Mike Snitzer <snitzer@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>