Fix condition for host managed voice SCO volume

After replacing STREAM_BT_SCO and not using the equivalent volume group
in APM, the flags isVoiceVolSrc and isBtScoVolSrc are not mutual
exclusive anymore. In order to check whether the voice volume is managed
by host it is now necessary to check the isBtScoVolSrc is false.

Test: manual
Flag: EXEMPT bugfix
Bug: 374151894
Change-Id: I3e29b86029cc89b3b78da8da2cbd5e1e31940c42