s390x/css: fix NULL handling for CCW addresses

Back then in the time of df1fe5bb ("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 2dc95b4c
("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: NHalil Pasic <pasic@linux.vnet.ibm.com>
Fixes: 2dc95b4c "s390x/3270: 3270 data stream handling"
Message-Id: <20170908152446.14606-3-pasic@linux.vnet.ibm.com>
Signed-off-by: NCornelia Huck <cohuck@redhat.com>

hw/s390x/css.c

@@ -793,7 +793,7 @@ static int css_interpret_ccw(SubchDev *sch, hwaddr ccw_addr,
     CCW1 ccw;
 
     if (!ccw_addr) {
-        return -EIO;
+        return -EINVAL; /* channel-program check */
     }
     /* Check doubleword aligned and 31 or 24 (fmt 0) bit addressable. */
     if (ccw_addr & (sch->ccw_fmt_1 ? 0x80000007 : 0xff000007)) {