ASoC: max98373-sdw: add missing memory allocation check

We forgot to test that devm_kcalloc doesn't return NULL.

Fixes: 349dd23931d1 ('ASoC: max98373: don't access volatile registers in bias level off')
Signed-off-by: Pierre-Louis Bossart <[e-mail]>
Reviewed-by: Guennadi Liakhovetski <[e-mail]>
Reviewed-by: Bard Liao <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

sound/soc/codecs/max98373-sdw.c

···
 	max98373->cache = devm_kcalloc(dev, max98373->cache_num,
 				       sizeof(*max98373->cache),
 				       GFP_KERNEL);
+	if (!max98373->cache)
+		return -ENOMEM;
 
 	for (i = 0; i < max98373->cache_num; i++)
 		max98373->cache[i].reg = max98373_sdw_cache_reg[i];