[sensor] Change log file timestamp unit to us

Changing sensor event timestamp unit from ms to us to help debugging
timestamp related cts failure.

Test: m cts && cts-tradefed run everything --module CtsSensorTestCases && \
      adb shell head /sdcard/sensorTests/events/*

Change-Id: I51460b95c2a873170b56fe7e17a4aa60447c68c0
1 file changed