Remove mId from DeviceDescriptor.

DeviceDescriptor inherits from AudioPort which has the correct
handle mId. The mId in DeviceDescriptor shadows this so calls
like DeviceVector::getDeviceFromId() findDeviceById fail because
they are looking at the wrong mId. The failure itself manifested
as createAudioPatch failing.

Change-Id: I8dd012d0678facaac84844b92226cc4b788abece