msi-laptop: make struct rfkill_ops const

rfkill uses a const struct rfkill_ops pointer.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: Lennart Poettering <mzxreary@0pointer.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Matthew Garrett <mjg@redhat.com>