nvme-pci: don't limit DMA segement size

NVMe uses PRPs (or optionally unlimited SGLs) for data transfers and
has no specific limit for a single DMA segement.  Limiting the size
will cause problems because the block layer assumes PRP-ish devices
using a virt boundary mask don't have a segment limit.  And while this
is true, we also really need to tell the DMA mapping layer about it,
otherwise dma-debug will trip over it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>