s390x/css: fix NULL handling for CCW addresses

Back then in the time of df1fe5bb49 ("s390: Virtual channel subsystem
support.", 2013-01-24) -EIO used to map to a channel-program check (via
the default label of the switch statement).  Then 2dc95b4cac
("s390x/3270: 3270 data stream handling", 2016-04-01) came along
and that changed dramatically.

Let us roll back this undesired side effect, and go back to
channel-program check.

Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Fixes: 2dc95b4cac "s390x/3270: 3270 data stream handling"
Message-Id: <20170908152446.14606-3-pasic@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
