sony-laptop: warn on multiple KBD backlight handles

Some BIOS versions/Vaio models apparently ship with two nearly identical
functions to handle backlight related controls.
The only difference seems to be:
        If (LEqual (BUF1, 0x40))
        {
            Store (0x40, P80H)
            Store (BUF2, Local0)
-           And (Local0, One, Local0)
+           And (Local0, 0x03, Local0)
            Store (Local0, ^^H_EC.KLPC)
        }

Avoid erroring out on initialization and messing things up on cleanup
for now since we never call into these methods with anything different
than 1 or 0.
This issue was found on a Sony VPCSE1V9E/BIOS R2087H4.

Cc: Marco Krüger <krgsch@gmail.com>
Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>