dmaengine: hsu: speed up residue calculation

There is no need to calculate an overall length of the descriptor each time we
call for DMA transfer status. Instead we do this at descriptor allocation stage
and keep the stored length for further usage.

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

drivers/dma/hsu/hsu.h

@@ -65,6 +65,7 @@ struct hsu_dma_desc {
 	enum dma_transfer_direction direction;
 	struct hsu_dma_sg *sg;
 	unsigned int nents;
+	size_t length;
 	unsigned int active;
 	enum dma_status status;
 };