AudioService: Fix absolute volume for AVRCP

Avrcp.java uses max volume obtained by getStreamMaxVolume() when
converting to AVRCP levels and it returns non-scaled volume index.
For this reason volume index needs to be dispatched to Avrcp before
scaling as otherwise Avrcp will convert volume level incorrectly,
i.e. max volume index for music stream is 15 and any volume index
>1 (>10 after scaling) will result in setting *MAXIMUM* volume level
on headset which is not safe for listener.

https://android-review.googlesource.com/#/c/87670/