Fix a crash in SystemUI when using CarNavigationBar.

CarNavigationBar overrides getCurrentView() in phone NavigationBarView
but the dump() method in NavigationBarView uses mCurrentView directly,
which may be null in the auto case. Callign getCurrentView() returns
the correct overriden view.

This patch makes the change to dump() to use getCurrentView().

Bug: 27046536
Change-Id: I92e5655325247d27faac1e33d8622783652bdb10