eeepc-laptop: fix hotplug_disabled module_param permissions

The hotplug_disabled module parameter is determinated at the module load
time.  Change the value after the module is loaded does not make sense and
has no effect at all, thus set the permissions to 0444 instead of 0644.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Corentin Chary <corentincj@iksaif.net>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Matthew Garrett <mjg@redhat.com>