AudioProductStrategy: fix attributesMatches()

Use AudioAttributes.getSystemUsage() instead of getUsage()
when comparing attributes as getUsage() defaults to UNKNOWN for
system usages and causes a false match.

Bug: 136121584
Test: build & run cts-dev -m CtsMediaTestCase --test android.media.cts.AudioProductStrategyTest
Change-Id: I377e840b18443c33fb0b562b27fbc706aaeb8055