dmaengine: pch_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/pch_dma.c

@@ -357,14 +357,13 @@ static void pdc_chain_complete(struct pch_dma_chan *pd_chan,
 			       struct pch_dma_desc *desc)
 {
 	struct dma_async_tx_descriptor *txd = &desc->txd;
-	dma_async_tx_callback callback = txd->callback;
-	void *param = txd->callback_param;
+	struct dmaengine_desc_callback cb;
 
+	dmaengine_desc_get_callback(txd, &cb);
 	list_splice_init(&desc->tx_list, &pd_chan->free_list);
 	list_move(&desc->desc_node, &pd_chan->free_list);
 
-	if (callback)
-		callback(param);
+	dmaengine_desc_callback_invoke(&cb, NULL);
 }
 
 static void pdc_complete_all(struct pch_dma_chan *pd_chan)