Simplify code and fix race condition caused by registering
hwmon device prior to creating sysfs attributes.

Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>