SG: Change sg_set_page() to take length and offset argument

Most drivers need to set length and offset as well, so may as well fold
those three lines into one.

Add sg_assign_page() for those two locations that only needed to set
the page, where the offset/length is set outside of the function context.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/drivers/infiniband/hw/mthca/mthca_memfree.c b/drivers/infiniband/hw/mthca/mthca_memfree.c
index 007b381..1f4d27d 100644
--- a/drivers/infiniband/hw/mthca/mthca_memfree.c
+++ b/drivers/infiniband/hw/mthca/mthca_memfree.c
@@ -113,9 +113,7 @@
 	if (!page)
 		return -ENOMEM;
 
-	sg_set_page(mem, page);
-	mem->length = PAGE_SIZE << order;
-	mem->offset = 0;
+	sg_set_page(mem, page, PAGE_SIZE << order, 0);
 	return 0;
 }
 
@@ -481,9 +479,8 @@
 	if (ret < 0)
 		goto out;
 
-	sg_set_page(&db_tab->page[i].mem, pages[0]);
-	db_tab->page[i].mem.length = MTHCA_ICM_PAGE_SIZE;
-	db_tab->page[i].mem.offset = uaddr & ~PAGE_MASK;
+	sg_set_page(&db_tab->page[i].mem, pages[0], MTHCA_ICM_PAGE_SIZE,
+			uaddr & ~PAGE_MASK);
 
 	ret = pci_map_sg(dev->pdev, &db_tab->page[i].mem, 1, PCI_DMA_TODEVICE);
 	if (ret < 0) {