hwmon: (nct6683) Add missing sysfs attribute initialization

hwmon: (nct6683) Add missing sysfs attribute initialization

The following error message is seen when loading the nct6683 driver
with DEBUG_LOCK_ALLOC enabled.

BUG: key ffff88040b2f0030 not in .data!
------------[ cut here ]------------
WARNING: CPU: 0 PID: 186 at kernel/locking/lockdep.c:2988
				lockdep_init_map+0x469/0x630()
DEBUG_LOCKS_WARN_ON(1)

Caused by a missing call to sysfs_attr_init() when initializing
sysfs attributes.

Reported-by: Alexey Orishko <[email protected]>
Reviewed-by: Jean Delvare <[email protected]>
Cc: [email protected] # v3.18+
Signed-off-by: Guenter Roeck <[email protected]>