Fix reference frame size restrictions.
The issue was introduced by commit g9f37d149 with adding explicit restrictions on reference-frame scale factors. The restriction is checked against aligned-by-8 frame dimensions, not against original ones. So, for example, frame of 35×35 actually can refer to frame of 70×70, but the new check won't allow this. It will compare 35 vs 72 (not 70), so 2x downscale limit will be exceeded. Change-Id: Ic663693034440f64ac8312cbff9e1e773a921060