nvme: add proper discard setup for the multipath device

nvme: add proper discard setup for the multipath device

Add a gendisk argument to nvme_config_discard so that the call to
nvme_update_disk_info for the multipath device node updates the
proper request_queue.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Tested-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>