nvme-pci: Set the prp2 correctly when using more than 4k page

commit a4f40484 upstream.

In the current code, the nvme is using a fixed 4k PRP entry size,
but if the kernel use a page size which is more than 4k, we should
consider the situation that the bv_offset may be larger than the
dev->ctrl.page_size. Otherwise we may miss setting the prp2 and then
cause the command can't be executed correctly.

Fixes: dff824b2

 ("nvme-pci: optimize mapping of small single segment requests")
Cc: stable@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>