PM / Sleep: Correct inaccurate information in devices.txt

The documentation file Documentation/power/devices.txt contains some
information that isn't correct any more due to code modifications
made after that file had been created (or updated last time).  Fix
this.

Change-Id: I82431a720178c2973e7a61b3bdbaaeccd758b42b
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>