z8530_dma_status - Handle a DMA status exception
void z8530_dma_status (struct z8530_channel *chan);
chan Z8530 channel to process
A status event occurred on the Z8530. We receive these for two reasons when in DMA mode. Firstly if we finished a packet transfer we get one and kick the next packet out. Secondly we may see a DCD change and have to poke the protocol layer.