Fix profile saver reference point when calculating the sleep time

It is wrong to use last_time_ns_saver_woke_up_ as a reference. We should
use sleep_start.

Bug: 28953776

(cherry picked from commit dc85bd757e7f27c38143536a9f4fa4c2c7d07272)

Change-Id: I400502c76a0423190826bbf1bd8e552cf591ebc3
1 file changed