pktcdvd: removing device does not remove its sysfs dir

This is the counterpart to cba76717
("pktcdvd: remove broken dev_t export of class devices").  Device is not
registered using dev_t, so it should not be destroyed using device_destroy
which looks up the device by dev_t.  This will fail and adding the device
again will fail with the "duplicate name" error.  This is fixed using
device_unregister instead of device_destroy.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Peter Osterlund <petero2@telia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>