power: Documentation: Update s2ram link

The s2ram link is broken because there is a new OpenSuse wiki online.
The page does no longer exist, it was merged in the Suspend_to_RAM
page.

Signed-off-by: Jens Frederich <jfrederich@gmail.com>
Acked-by: Rob Landley <rob@landley.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>