fix audio patch leak.

Always wait for status when executing a create audio patch
command in audio policy service command thread.
The returned patch handle must be passed back to audio policy manager
so that the patch can be modified later.
Failing to do so causes a leak of patch descriptors in audio flinger.

Bug: 19032387.
Change-Id: I5462d1437fac244d9c5e38f2c7b8e1a4c01d2b75