asus-nb-wmi: Constify asus_quirks[] DMI table

Constify the asus_quirks[] DMI table. There's no need to have it
writeable during runtime.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Corentin Chary <corentin.chary@gmail.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>