ASoC: Tegra: Fix error handling in DMA channel alloc

tegra_dma_allocate_channel() returns NULL on errors, not an error pointer.
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/tegra/tegra_pcm.c

@@ -161,8 +161,8 @@ static int tegra_pcm_open(struct snd_pcm_substream *substream)
 	prtd->dma_req[1].dev = prtd;
 
 	prtd->dma_chan = tegra_dma_allocate_channel(TEGRA_DMA_MODE_ONESHOT);
-	if (IS_ERR(prtd->dma_chan)) {
-		ret = PTR_ERR(prtd->dma_chan);
+	if (prtd->dma_chan == NULL) {
+		ret = -ENOMEM;
 		goto err;
 	}