ata: ep93xx: use dmaengine_prep_slave_sg api instead of internal callback

it is better to use generic api instead of calling an internal callback
like channel->device->device_prep_slave_sg().

Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

drivers/ata/pata_ep93xx.c

@@ -708,8 +708,8 @@ static void ep93xx_pata_dma_start(struct ata_queued_cmd *qc)
 	struct dma_chan *channel = qc->dma_dir == DMA_TO_DEVICE
 		? drv_data->dma_tx_channel : drv_data->dma_rx_channel;
 
-	txd = channel->device->device_prep_slave_sg(channel, qc->sg,
-		 qc->n_elem, qc->dma_dir, DMA_CTRL_ACK, NULL);
+	txd = dmaengine_prep_slave_sg(channel, qc->sg, qc->n_elem, qc->dma_dir,
+		DMA_CTRL_ACK);
 	if (!txd) {
 		dev_err(qc->ap->dev, "failed to prepare slave for sg dma\n");
 		return;