Fixed 4-channel audio DMA issue.
Fixed 4-channel audio DMA issue.

- SAI DMA request is asserted as long as either channel FIFO is below
  the watermark. This causes the first DMA channel to retrigger its
  minor loop, which then retriggers the second DMA channel's minor loop.
  The data from the extra minor loops was being lost because the SAI
  FIFOs were already full.
- Setting the minor loops to transfer half as much data solves the issue
  by taking into account that two minor loops will execute for each DMA
  request.

flit/modular,flit/modular,flit/modular,flit/modular,flit/modular