[Flexiglass] Fix the height of HUNs in QuickSettings

HUNs had a negative height, when they were displayed in the
QuickSettings, because we've calculated it wrong.

Bug: 339181697
Test: check the height of HUNs in QuickSettings
Test: atest StackScrollAlgorithmTest
Flag: com.android.systemui.scene_container
Change-Id: I853be7d7c367b957f28d3a999f75d8207737221d