ACodec: Fix error handling in OutputPortSettingsChangedState

Freeing the input buffers & node in ACodec::OutputPortSettingsChangedState
on error, can cause NuPlayerDecoder to deference freed buffers.
Instead of freeing the node internally on error in
OutputPortSettingsChangedState, notify error to NuPlayer, and add
kWhatShutDown handling to initiate Idle state transition.

Change-Id: I7778d759c564fad27d266ac63d293bf0c30c029b