VolumeShaper: API change for duration

Time in milliseconds is a long.
Update API to not specify the unit in the setter/getter for
  the VolumeShaper duration.

Test: cts-tradefed run cts CtsMediaTestCases -t android.media.cts.VolumeShaperTest

Change-Id: If5f95cc43418d831105cbef2c43b6e9cfcf9082b