nvme-pci: replace NVME_MAX_KB_SZ with NVME_MAX_BYTE

Having a define in kiB units is a bit weird.  Also update the
comment now that there is not scatterlist limit.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Daniel Gomez <da.gomez@samsung.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/20250625113531.522027-8-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>