dmaengine: idma64: convert idma64_hw_desc_fill() to return void

Explicitly show in idma64_desc_fill() how we link the hardware
descriptors.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>