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 <[e-mail]>
Fixes: 08ebc9def79fc ("hwmon: Add Congatec Board Controller monitoring driver")
Reviewed-by: Thomas Richard <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>

drivers/hwmon/cgbc-hwmon.c

···
 	nb_sensors = data[0];
 
 	hwmon->sensors = devm_kzalloc(dev, sizeof(*hwmon->sensors) * nb_sensors, GFP_KERNEL);
+	if (!hwmon->sensors)
+		return -ENOMEM;
+
 	sensor = hwmon->sensors;
 
 	for (i = 0; i < nb_sensors; i++) {