pkt_setup_dev() expects module reference to be held on invocation.
This used to be true for sysfs callbacks but not anymore.  Test and
grab module reference around pkt_setup_dev() in
class_pktcdvd_store_add().
Signed-off-by: NTejun Heo <htejun@gmail.com>
Acked-by: NPeter Osterlund <petero2@telia.com>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>