Only log smartspace timers when value changes

The value is logged every time the device locks as communal gets ready,
so only log when the value changes to avoid spamming the buffer with
empty list logs when there are no timers.

Bug: N/A
Test: N/A, verified locally via logcat
Flag: NONE small logging change
Change-Id: Ic3cbce5652d8f31123618e5df32694dff10c41c0