SystemUI: Correct settings observer usage

Settings observer was already created by a global variable, but
it was never used and instead a new one was created in start().

Corrected the code to utilize the already created settings observer.

Change-Id: I337ce12bf32f0355f6280f7b74767e5eb17438a6
Signed-off-by: Evan Anderson <evan@thelinuxman.us>
Merge "SystemUI: Correct settings observer usage" into kitkat