Fix StatusBarMobileView to use correct shade

As SignalDrawable now uses a single color to draw, it should get
DualToneHandler#getSingleColor passed to it.

Test: manual on QS Header and launcher (white background). The shade of
gray matches the other icons.
Fixes: 133258347

Change-Id: Id9e324623d0e82753b1a31a7908df9399e75c827