Must set the ATAPI device signature, see ATA4 8.27.5.2 Outputs for
PACKET Command feature set devices, and ACS-2 7.36.6 Outputs for
PACKET feature set devices.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>