nvme-pci: rework the build time assert for NVME_MAX_NR_DESCRIPTORS

The current use of an always_inline helper is a bit convoluted.
Instead use macros that represent the arithmetics used for building
up the PRP chain.

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/20250625113531.522027-9-hch@lst.de


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