Write unity gain back with successful EFFECT_CMD_SET_VOLUME handling

Bug: 271500140
Test: Enable AIDL and flash to pixel
Test: Play Youtube music with effect on/off
Change-Id: I7e37a289f9c5f7773e500e59220963d1d17b5fb2
Merged-In: I7e37a289f9c5f7773e500e59220963d1d17b5fb2
(cherry picked from commit 1cd7cb9e3f6b84aa5d1f7d1a77704dbbdc912c4d)
1 file changed