SystemUI: Fix QS mobile icon disappearing on theme switch

When there is only single SIM, the signal icon disappears
from expanded QS header on switching dark theme QS tile.
Ensure that the signal icon is always shown on single SIM.

Change-Id: I089731fe5815a0b2bcbbed1002ca65aa5d3301cd
Signed-off-by: Adithya R <gh0strider.2k18.reborn@gmail.com>