media: rcar_drif: 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.

By using dma_request_chan() directly the driver can support deferred
probing against DMA.

Signed-off-by: Peter Ujfalusi <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/platform/rcar_drif.c

···
 	for_each_rcar_drif_channel(i, &sdr->cur_ch_mask) {
 		struct rcar_drif *ch = sdr->ch[i];
 
-		ch->dmach = dma_request_slave_channel(&ch->pdev->dev, "rx");
-		if (!ch->dmach) {
+		ch->dmach = dma_request_chan(&ch->pdev->dev, "rx");
+		if (IS_ERR(ch->dmach)) {
 			rdrif_err(sdr, "ch%u: dma channel req failed\n", i);
-			ret = -ENODEV;
+			ret = PTR_ERR(ch->dmach);
 			goto dmach_error;
 		}