Fixed non-resetting scroll state

Made scroll state reset for end side panel  whenever another category is
selected.

Fix: 362737826
Flag: com.android.systemui.keyboard_shortcut_helper_rewrite
Test: Manual - navigate through shortcut helper, scroll through
shortcuts, navigate to another category, ensure that shortcut panel is scrolled to
the top.

Change-Id: I19b1713c0973b1422feb2c205d77af3e9b526e44