platform: x86: asus_acpi: world-writable procfs files

Don't allow everybody to change ACPI settings.  The comment says that it
is done deliberatelly, however, the comment before disp_proc_write()
says that at least one of these setting is experimental.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>