kmsaudiomixer: release requested pads
kmsaudiomixer: release requested pads

Change-Id: I30862812f5a6ae937a073aec21569f84aa50175b

ESTOS/kms-core,shelsonjava/kms-core,KurentoLegacy/gst-kurento-plugins,TribeMedia/kms-core,shelsonjava/kms-core,KurentoLegacy/gst-kurento-plugins,TribeMedia/kms-core,ESTOS/kms-core,KurentoLegacy/gst-kurento-plugins,Kurento/kms-core,shelsonjava/kms-core,ESTOS/kms-core,ESTOS/kms-core,Kurento/kms-core,shelsonjava/kms-core,Kurento/kms-core,TribeMedia/kms-core,TribeMedia/kms-core,KurentoLegacy/gst-kurento-plugins,Kurento/kms-core