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/scsi/ipr.c b/drivers/scsi/ipr.c
index 439b97a..0841df0 100644
--- a/drivers/scsi/ipr.c
+++ b/drivers/scsi/ipr.c
@@ -2890,7 +2890,7 @@
 			return NULL;
 		}
 
-		sg_set_page(&scatterlist[i], page);
+		sg_set_page(&scatterlist[i], page, 0, 0);
 	}
 
 	return sglist;