ASoC: simple-card-utils: test memory allocation

li->conf will be 0 if it was not DPCM case.
Then, 1) we shouldn't call devm_kcalloc() with size 0,
2) we need NULL pointer check if li->conf was not 0.
This patch fixed above issues.
Special thanks to Pierre-Louis Bossart

Reported-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>