dmaengine: mmp_pdma: 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 <[e-mail]>
Reviewed-by: Lars-Peter Clausen <[e-mail]>
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/mmp_pdma.c

···
 	struct mmp_pdma_desc_sw *desc, *_desc;
 	LIST_HEAD(chain_cleanup);
 	unsigned long flags;
+	struct dmaengine_desc_callback cb;
 
 	if (chan->cyclic_first) {
-		dma_async_tx_callback cb = NULL;
-		void *cb_data = NULL;
-
 		spin_lock_irqsave(&chan->desc_lock, flags);
 		desc = chan->cyclic_first;
-		cb = desc->async_tx.callback;
-		cb_data = desc->async_tx.callback_param;
+		dmaengine_desc_get_callback(&desc->async_tx, &cb);
 		spin_unlock_irqrestore(&chan->desc_lock, flags);
 
-		if (cb)
-			cb(cb_data);
+		dmaengine_desc_callback_invoke(&cb, NULL);
 
 		return;
 	}
···
 		/* Remove from the list of transactions */
 		list_del(&desc->node);
 		/* Run the link descriptor callback function */
-		if (txd->callback)
-			txd->callback(txd->callback_param);
+		dmaengine_desc_get_callback(txd, &cb);
+		dmaengine_desc_callback_invoke(&cb, NULL);
 
 		dma_pool_free(chan->desc_pool, desc, txd->phys);
 	}