sony-laptop: improve SNC initialization and acpi notify callback code

Loop through the list of SNC handles and run the proper initialization
function for each of the known handles. Also return void in function
where we are not checking the return value anyway.
For notifications we also know which handle is linked to the event and
the code becomes simpler to read with a switch rather than using
convoluted ifs.

[malattia@linux.it: Code reworked to merge the initialization code
improvements and the notify callback changes. Modified the code paths to
allow easier error exit paths.  Also fixed some missing break statements
and spelling mistakes.]

Signed-off-by: Marco Chiappero <marco@absence.it>
Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Matthew Garrett <mjg@redhat.com>