dmaengine: ep93xx_dma: convert callback to helper function

This is in preperation of moving to a callback that provides results to the
callback for the transaction. The conversion will maintain current behavior
and the driver must convert to new callback mechanism at a later time in
order to receive results.
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/ep93xx_dma.c

@@ -739,10 +739,10 @@ static void ep93xx_dma_tasklet(unsigned long data)
 {
 	struct ep93xx_dma_chan *edmac = (struct ep93xx_dma_chan *)data;
 	struct ep93xx_dma_desc *desc, *d;
-	dma_async_tx_callback callback = NULL;
-	void *callback_param = NULL;
+	struct dmaengine_desc_callback cb;
 	LIST_HEAD(list);
 
+	memset(&cb, 0, sizeof(cb));
 	spin_lock_irq(&edmac->lock);
 	/*
 	 * If dma_terminate_all() was called before we get to run, the active
@@ -757,8 +757,7 @@ static void ep93xx_dma_tasklet(unsigned long data)
 				dma_cookie_complete(&desc->txd);
 			list_splice_init(&edmac->active, &list);
 		}
-		callback = desc->txd.callback;
-		callback_param = desc->txd.callback_param;
+		dmaengine_desc_get_callback(&desc->txd, &cb);
 	}
 	spin_unlock_irq(&edmac->lock);
 
@@ -771,8 +770,7 @@ static void ep93xx_dma_tasklet(unsigned long data)
 		ep93xx_dma_desc_put(edmac, desc);
 	}
 
-	if (callback)
-		callback(callback_param);
+	dmaengine_desc_callback_invoke(&cb, NULL);
 }
 
 static irqreturn_t ep93xx_dma_interrupt(int irq, void *dev_id)