s390/cio: Update purge function to unregister the unused subchannels

commit 9daa5a87 upstream.

Starting with 'commit 2297791c ("s390/cio: dont unregister
subchannel from child-drivers")', cio no longer unregisters
subchannels when the attached device is invalid or unavailable.

As an unintended side-effect, the cio_ignore purge function no longer
removes subchannels for devices on the cio_ignore list if no CCW device
is attached. This situation occurs when a CCW device is non-operational
or unavailable

To ensure the same outcome of the purge function as when the
current cio_ignore list had been active during boot, update the purge
function to remove I/O subchannels without working CCW devices if the
associated device number is found on the cio_ignore list.

Fixes: 2297791c ("s390/cio: dont unregister subchannel from child-drivers")
Suggested-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>