Fix AUDIO_TIMESTRETCH_STRETCH value name

There used to be a discrepancy between the name of the enum
constant between HAL, system/audio.h, and PlaybackParams.java.

The constant should be named AUDIO_TIMESTRETCH_STRETCH_VOICE
to match Java and HAL.

Bug: 122858783
Test: m
Change-Id: Ief4d5df482dc7eee710aaa7d2d0ccec422246553
Merged-In: Ief4d5df482dc7eee710aaa7d2d0ccec422246553