For a front merge, the maximum number of sectors of the
request must be checked against the front merge BIO sector,
not the current sector of the request.
Signed-off-by: Damien Le Moal <damien.lemoal@hgst.com> Reviewed-by: Hannes Reinecke <hare@suse.com> Signed-off-by: Jens Axboe <axboe@fb.com>