Fixed the bubble bar drop zone height calculation.

Updated the calculation for the bubble bar drop zone height.

Bug: 396476450
Flag: com.android.wm.shell.enable_create_any_bubble
Test: Manual. Drag an app icon from the taskbar over the bubble bar drop
zone until the drop target appears. Drag the icon up out of the drop
zone; the drop target disappears.

Change-Id: Idcb6e45ee1328fa76ee24d9354769764c51601b3