ata: pata_arasan_cf: Use dma_request_chan() instead dma_request_slave_channel()

dma_request_slave_channel() is a wrapper on top of dma_request_chan()
eating up the error code.

The dma_request_chan() is the standard API to request slave channel,
clients should be moved away from the legacy API to allow us to retire
them.
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/ata/pata_arasan_cf.c

@@ -526,9 +526,10 @@ static void data_xfer(struct work_struct *work)
 
 	/* request dma channels */
 	/* dma_request_channel may sleep, so calling from process context */
-	acdev->dma_chan = dma_request_slave_channel(acdev->host->dev, "data");
-	if (!acdev->dma_chan) {
+	acdev->dma_chan = dma_request_chan(acdev->host->dev, "data");
+	if (IS_ERR(acdev->dma_chan)) {
 		dev_err(acdev->host->dev, "Unable to get dma_chan\n");
+		acdev->dma_chan = NULL;
 		goto chan_request_fail;
 	}
 
@@ -539,6 +540,7 @@ static void data_xfer(struct work_struct *work)
 	}
 
 	dma_release_channel(acdev->dma_chan);
+	acdev->dma_chan = NULL;
 
 	/* data xferred successfully */
 	if (!ret) {