audio policy: rescale volume index in setStreamVolumeIndex

Fix a problem in setStreamVolumeIndex() introduced by commit dcd4ab18
where stream volumes where applied systematically when in call for
all streams regardless of streamsMatchForvolume().
Also add index rescaling as in theory two streams matching for volume
do not have necessarily the same index range.

Bug: 111194621
Test: repro steps in bug.
Change-Id: I713b35921d4df19b521fc98281636a9c17483998