dm: stop using blk_limits_io_{min,opt}

Remove use of the blk_limits_io_{min,opt} and assign the values directly
to the queue_limits structure.  For the io_opt this is a completely
mechanical change, for io_min it removes flooring the limit to the
physical and logical block size in the particular caller.  But as
blk_validate_limits will do the same later when actually applying the
limits, there still is no change in overall behavior.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>