sony-laptop: Avoid oops on module unload for older laptops

Older VAIO laptops without the SN00 ACPI method will have the "handles"
variable unset. Return early from sony_nc_function_cleanup when "handles"
is null.

Signed-off-by: Lawrence Yiu <lawyiu.dev@gmail.com>
Acked-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>