aaudio: fix IsochronousClockModel drift calculation

Correct an error that caused the timing window to jump
forward in time by one burst when a late timestamp was detected.

Bug: 133513175
Bug: 122680738
Bug: 123643363
Test: aaudio_loopback -tm -s20
Change-Id: I65c05d2ab123bcd347cb900de055c49c0c9beada