audioflinger: fix missing track metadata

PatchTrack do not have audio attributes, so source meta data
usage must be derived from the stream type communicated
when the SW bridge audio patch is created.

Test: make.
Merged-In: I53c8ad41c1ce7266beff0362f576d2d07dd61ad5
Change-Id: I53c8ad41c1ce7266beff0362f576d2d07dd61ad5