iio: mma8452: use runtime pm instead of device specific autosleep

What is this autosleep?
-----------------------
It slows down the device after x seconds of inactivity. The thing is, we have
really achieved almost the same by runtime pm.

differnces are:

autosleep
* uses more power during inactivity
* the first read after inactivity slightly faster
* complicated to understand for the user
* no documented sysfs interface (afaik)
* complicated to read and maintain

runtime pm
* already merged in mma8452
* uses less power during inactivity
* first read after inactivity slower
* easy to use. well documented.
* easy to maintain and understand

The two approaches solve the same problem. runtime pm has more advantages
than autosleep and comes quite close to it's behaviour anyways. As I see it,
autosleep, even if somehow supported, would never be used anyways.

So resolve this issue by "ignoring" autosleep.

Signed-off-by: Martin Kepplinger <[e-mail]>
Reviewed-by: Martina Kepplinger <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/accel/mma8452.c

···
  *
  * 7-bit I2C slave address 0x1c/0x1d (pin selectable)
  *
- * TODO: orientation events, autosleep
+ * TODO: orientation events
  */
 
 #include <linux/module.h>