nvme-pci: clear the prp2 field when not used

If the prp2 field is not filled in nvme_setup_prp_simple(), the prp2
field is garbage data. According to nvme spec, the prp2 is reserved if
the data transfer does not cross a memory page boundary, so clear it to
zero if it is not used.
Signed-off-by: NLei Rao <lei.rao@intel.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

drivers/nvme/host/pci.c

@@ -797,6 +797,8 @@ static blk_status_t nvme_setup_prp_simple(struct nvme_dev *dev,
 	cmnd->dptr.prp1 = cpu_to_le64(iod->first_dma);
 	if (bv->bv_len > first_prp_len)
 		cmnd->dptr.prp2 = cpu_to_le64(iod->first_dma + first_prp_len);
+	else
+		cmnd->dptr.prp2 = 0;
 	return BLK_STS_OK;
 }