hwmon: (applesmc) Simplify feature sysfs handling

Given the dynamic node construction method, the setup of the
accelerometer, light sensor and keyboard backlight sysfs nodes
can be simplified. This patch does not contain any logic changes.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>