Update DSP playback (old) to avoid reinitializing audio again if audio
is still playing from the last time. In other words, if a single cycle
audio block from DSP command 0x14 is in progress on playback, and
another DSP command 0x14 comes in before the current block is finished,
then just reset the DMA left/total values so the audio playback moves on
uninterrupted.

Sound Blaster output from Crystal Dream is now flawless, and sounds just
like it did on real hardware.