Function DecodeSBRBitstream

* Function: DecodeSBRBitstream * * Description: decode sideband information for SBR * * Inputs: base output channel (range = [0, nChans-1]) * * Outputs: initialized state structs (SBRHdr, SBRGrid, SBRFreq, SBRChan) * * Return: 0 if successful, error code (< 0) if error * * Notes: SBR payload should be in aacDecInfo->fillBuf * returns with no error if