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>
Signed-off-by: Len Brown <len.brown@intel.com>