NVMe: Fix off-by-one when filling in PRP lists

If the last element in the PRP list fits on the end of the page, there's
no need to allocate an extra page to put that single element in.  It can
fit on the end of the page.
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>

drivers/block/nvme.c

@@ -376,12 +376,13 @@ static struct nvme_prps *nvme_setup_prps(struct nvme_dev *dev,
 	cmd->prp2 = cpu_to_le64(prp_dma);
 	i = 0;
 	for (;;) {
-		if (i == PAGE_SIZE / 8 - 1) {
+		if (i == PAGE_SIZE / 8) {
 			__le64 *old_prp_list = prp_list;
 			prp_list = dma_pool_alloc(pool, GFP_ATOMIC, &prp_dma);
 			prps->list[prp_page++] = prp_list;
-			old_prp_list[i] = cpu_to_le64(prp_dma);
-			i = 0;
+			prp_list[0] = old_prp_list[i - 1];
+			old_prp_list[i - 1] = cpu_to_le64(prp_dma);
+			i = 1;
 		}
 		prp_list[i++] = cpu_to_le64(dma_addr);
 		dma_len -= PAGE_SIZE;