ASoC: imx-pcm-dma: add NULL test

Add NULL test on call to devm_kzalloc.

The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression x;
@@

* x = devm_kzalloc(...);
  ... when != x == NULL
  *x
// </smpl>
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/fsl/imx-pcm-dma.c

@@ -62,6 +62,8 @@ int imx_pcm_dma_init(struct platform_device *pdev, size_t size)
 
 	config = devm_kzalloc(&pdev->dev,
 			sizeof(struct snd_dmaengine_pcm_config), GFP_KERNEL);
+	if (!config)
+		return -ENOMEM;
 	*config = imx_dmaengine_pcm_config;
 	if (size)
 		config->prealloc_buffer_size = size;