Fix SysUI / AoD leaking content observers

It will add one more setting observer when AOD state is changed from
DOZE_PULSING to DOZE/DOZE_AOD.

Avoid to register setting observer again when it has been registered
before.

For example: This issue will occur when receving notification in AOD.

Bug: 133388082
Test: atest SystemUITests
Change-Id: Ie3fccc4dd6ecc77692649ace401779b8398b63f8
2 files changed