audio policy: fix ringtone volume on headphones

When limiting ringtone volume because headphones are connected
and music is playing, the volume was not limited against the right
music volume. The is because the device used for music (headphone)
is not the same as the one used for ringtone (headphone + speaker).

Bug 6816207.

Change-Id: I3342be1789a1b7c58705812335b788f030bc6d76
1 file changed