pktcdvd: fix defective misuses of pkt_<level>

Fix thinkos where pkt_<level> needs a valid pktcdvd_device * and the
pointer is known to be NULL.

Signed-off-by: Joe Perches <joe@perches.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com> (go smatch!)
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>