Fixed an issue where heads up notifications would overlap

We recently fixed the logic where notifications are being displayed
if multiple huns are showing, however we were not clipping to them.
We're now clipping heads up notifications as well by the clipTopAmount

Fixes: 136914021
Test: add two different sized HUNS, so weird overlap.
Change-Id: I68a4c373eff3952b1a4711858c9ce61684f6ff17