nvme: fix max_segments integer truncation

nvme: fix max_segments integer truncation

The block layer uses an unsigned short for max_segments.  The way we
calculate the value for NVMe tends to generate very large 32-bit values,
which after integer truncation may lead to a zero value instead of
the desired outcome.

Signed-off-by: Christoph Hellwig <[email protected]>
Reported-by: Jeff Lien <[email protected]>
Tested-by: Jeff Lien <[email protected]>
Reviewed-by: Keith Busch <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>