Set output volume for routing device in startSource()

getNewOutputDevice selects a device by checking active strategy when
startSouce() is called. This behavior sometimes leads to set
unsupported device volume index. For example, BT A2DP resume from combo
output. a2dp output only supports A2DP sound devices. If sonification
stream is played via A2DP and Speaker during music playback, volume
index for speaker is applied as music volume when resume playback until
sonification stream is closed. At this time, A2DP device is selected as
routing device, so volume and routed device does not match.
To avoid this situation, setting volume index from supported device
in startSource().

Bug: 64053820
Test: Check volume after alarm sound finish during music playback via BT.
Change-Id: I71dae2c77d82abc0227ec45fc6c40bfd8f51c8c2