SystemUI: fix nav bar alignment with 4+ buttons

The menu button at the end is now a constant size,
so the separator in the front needs to also be constant now.

Change-Id: I83c33942509e6cf76750b806e828462f3df9c8a8
Signed-off-by: Roman Birg <romanbirg@gmail.com>

Conflicts:

	packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarView.java