dmaengine: mxs-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/mxs-dma.c

@@ -326,8 +326,7 @@ static void mxs_dma_tasklet(unsigned long data)
 {
 	struct mxs_dma_chan *mxs_chan = (struct mxs_dma_chan *) data;
 
-	if (mxs_chan->desc.callback)
-		mxs_chan->desc.callback(mxs_chan->desc.callback_param);
+	dmaengine_desc_get_callback_invoke(&mxs_chan->desc, NULL);
 }
 
 static int mxs_dma_irq_to_chan(struct mxs_dma_engine *mxs_dma, int irq)