nvmem: brcm_nvram: Add check for kzalloc

Add the check for the return value of kzalloc in order to avoid
NULL pointer dereference.

Fixes: 6e977eaa8280 ("nvmem: brcm_nvram: parse NVRAM content into NVMEM cells")
Cc: stable@vger.kernel.org
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20230127104015.23839-2-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
