sony-laptop: ignore missing _DIS method on pic device

At least the Vaio VGN-Z540N doesn't have this method, so let's not fail
to suspend just because it doesn't exist.

Signed-off-by: Adam Jackson <ajax@redhat.com>
Acked-by: Mattia Dongili <malattia@linux.it>
Cc: Len Brown <lenb@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>