audioflinger: Fix stream type for device->device patch

This logic got broken in ag/668511. The stream type was always
extracted from the 2nd patch source, which does not present
for device->device patches.

Test: MSD prototype, USB headset telecom calls in Pixel
Change-Id: Idc8314819010c3a315c5220785a4190e26e55b47
1 file changed