s390/cio: derive cdev information only for IO-subchannels

[ Upstream commit 0c3812c3 ]

cdev->online for the purge function must not be checked for the
non-IO subchannel type. Make sure that we are deriving the cdev only
from sch-type SUBCHANNEL_TYPE_IO.

Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Stable-dep-of: 1b607411 ("s390/cio: fix out-of-bounds access on cio_ignore free")
Signed-off-by: Sasha Levin <sashal@kernel.org>