[PATCH] nvme-pci: avoid 64-bit divisions in the HMB code

[Sagi Grimberg]

> [to be folded into "nvme-pci: implement host memory buffer support"]
> 
> Avoid 64-bit division by using shifts instead.  All involved sizez are
> powers of two.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>

Reviewed-by: Sagi Grimberg <sagi at grimberg.me>