[SG] Update drivers to use sg helpers

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 25b248a..3a8cd3d 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -1115,7 +1115,7 @@
 			}
 			prepare_request(req, io_req,
 					(unsigned long long) req->sector << 9,
-					sg->offset, sg->length, sg->page);
+					sg->offset, sg->length, sg_page(sg));
 
 			last_sectors = sg->length >> 9;
 			n = os_write_file(thread_fd, &io_req,