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>
Advanced reboot enabled by default (1/2)

Change-Id: Ie8ab34ecc532d14d296e33fa568e6cf3ebc681e8