hwmon: (cgbc-hwmon) Add missing NULL check after devm_kzalloc()

hwmon: (cgbc-hwmon) Add missing NULL check after devm_kzalloc()

The driver allocates memory for sensor data using devm_kzalloc(), but
did not check if the allocation succeeded. In case of memory allocation
failure, dereferencing the NULL pointer would lead to a kernel crash.

Add a NULL pointer check and return -ENOMEM to handle allocation failure
properly.

Signed-off-by: Li Qiang <liqiang01@kylinos.cn>
Fixes: 08ebc9def79fc ("hwmon: Add Congatec Board Controller monitoring driver")
Reviewed-by: Thomas Richard <thomas.richard@bootlin.com>
Link: https://lore.kernel.org/r/20251017063414.1557447-1-liqiang01@kylinos.cn
Signed-off-by: Guenter Roeck <linux@roeck-us.net>