rbd: BUG on invalid layout

This shouldn't actually be possible because the layout struct is
constructed from the RBD header and validated then.

[elder@inktank.com: converted BUG() call to equivalent rbd_assert()]
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>

drivers/block/rbd.c

@@ -1020,8 +1020,9 @@ static int rbd_do_request(struct request *rq,
 	layout->fl_stripe_count = cpu_to_le32(1);
 	layout->fl_object_size = cpu_to_le32(1 << RBD_MAX_OBJ_ORDER);
 	layout->fl_pg_pool = cpu_to_le32(rbd_dev->pool_id);
-	ceph_calc_raw_layout(osdc, layout, snapid, ofs, &len, &bno,
+	ret = ceph_calc_raw_layout(osdc, layout, snapid, ofs, &len, &bno,
 				   req, ops);
+	rbd_assert(ret == 0);
 
 	ceph_osdc_build_request(req, ofs, &len,
 				ops,