nvme: fix handling of large MDTS values

Instead of triggering an integer overflow and undefined behavior if MDTS is
large, set max_hw_sectors to UINT_MAX.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Keith Busch <kbusch@kernel.org>
[hch: rebased to account for the new nvme_mps_to_sectors helper]
Signed-off-by: Christoph Hellwig <hch@lst.de>