SamplingTimer: Fix issue with summary recording too much

The summary is supposed to just hold enough data to continue counting
once the device has reset. Since kernel stats reset when the device
resets, and the first update is ignored to account for soft resets where the
kernel continues running, SamplingTimer should not be recording the last value
it saw from /proc/wakelocks in the summary.

Bug:30575302
Change-Id: Ic193bc5af9a0ede514e3abc8146523d7316c47d3