ASoC: samsung: i2s: check the return value of kstrdup()

kstrdup() is a memory allocation function which can return NULL when
some internal memory errors happen. It is better to check the return
value of it to catch the error in time.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Xiaoke Wang <xkernel.wang@foxmail.com>
Link: https://lore.kernel.org/r/tencent_EC21778DC383823CBC4069EA9F0B84943905@qq.com


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