ASoC: max98373-sdw: add missing memory allocation check

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

Fixes: 349dd239 ('ASoC: max98373: don't access volatile registers in bias level off')
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Reviewed-by: Bard Liao <bard.liao@intel.com>
Link: https://lore.kernel.org/r/20210607222239.582139-2-pierre-louis.bossart@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>