audio flinger: clear possible stale audio patch on inputs and outputs

In PatchPanel::createAudioPatch() verify that when creating a patch with
an output or input mixer as source or sink, no patch with the
same output or input mixer remains in the patch list.
This will prevent a call to releaseAudioPatch(() received
later with a stale patch handle due to delayed request to clear current
output or input routing.

Test: play music and insert USB headset.
Change-Id: I9417bf061f5ef1d93cf3871a9ed51ee2b6ae62ef