ASoC: imx-pcm-dma: check kzalloc return value in function snd_imx_open

It fixed smatch warning:
sound/soc/fsl/imx-pcm-dma.c:112 snd_imx_open() error: potential null dereference 'dma_data'.  (kzalloc returns null)
Signed-off-by: Richard Zhao <richard.zhao@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

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

@@ -109,6 +109,9 @@ static int snd_imx_open(struct snd_pcm_substream *substream)
 	dma_params = snd_soc_dai_get_dma_data(rtd->cpu_dai, substream);
 
 	dma_data = kzalloc(sizeof(*dma_data), GFP_KERNEL);
+	if (!dma_data)
+		return -ENOMEM;
+
 	dma_data->peripheral_type = dma_params->shared_peripheral ?
 					IMX_DMATYPE_SSI_SP : IMX_DMATYPE_SSI;
 	dma_data->priority = DMA_PRIO_HIGH;