ASoC: rt5677: Add missing null check for failed allocation of rt5677_dsp

The allocation of rt5677_dsp can potentially fail and return null, so add
a null check and return -ENOMEM on a memory allocation failure.

Addresses-Coverity: ("Dereference null return")
Fixes: a0e0d135 ("ASoC: rt5677: Add a PCM device for streaming hotword via SPI")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20191024124610.18182-1-colin.king@canonical.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/rt5677-spi.c

@@ -376,6 +376,8 @@ static int rt5677_spi_pcm_probe(struct snd_soc_component *component)
 
 	rt5677_dsp = devm_kzalloc(component->dev, sizeof(*rt5677_dsp),
 			GFP_KERNEL);
+	if (!rt5677_dsp)
+		return -ENOMEM;
 	rt5677_dsp->dev = &g_spi->dev;
 	mutex_init(&rt5677_dsp->dma_lock);
 	INIT_DELAYED_WORK(&rt5677_dsp->copy_work, rt5677_spi_copy_work);