Only present through ccw bus.

[mkp: applied by hand]

Cc: Matthias Rudolph <Matthias.Rudolph@hitachivantara.com>
Cc: Takahiro Yasui <takahiro.yasui@hitachivantara.com>
Cc: Anthony Cheung <anthony.cheung@hpe.com>
Cc: Mike Christie <mchristi@redhat.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: James E.J. Bottomley <jejb@linux.vnet.ibm.com>
Cc: s390 ML <linux-s390@vger.kernel.org>
Cc: SCSI ML <linux-scsi@vger.kernel.org>
Cc: device-mapper development <dm-devel@redhat.com>
Signed-off-by: Xose Vazquez Perez <xose.vazquez@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>