audio policy: fix call volume

Fix setGroupVolumeIndex() which was applying
volume for all groups if in call and causing the wrong
index to be used.
when DTMF are muted when entering call, voice call was
also muted.

Bug: 128499415
Test: call with voice volume set to 6
Change-Id: Ie1296a7a48fdfba3710acb3d7a7e4f00e7b576a5