harmonize output scaling in combined formats

The scalling of the signal is handled incnsistently in the combined formats OSBA and OMASA. OSBA currently applies a factor of 0.5 to both input signals to avoid clipping. According to the ongoing discussions the passthrough modes of the codec should always preserve the loudness of the input. Additionally OSBA and OMASA should exhibit consistent behavior. This issue shall track the changes required to achieve this.