docs/s390x: fix vfio-ccw type

Fix the type name in the mdevctl example.
Signed-off-by: NCornelia Huck <cohuck@redhat.com>
Reviewed-by: NEric Farman <farman@linux.ibm.com>
Message-Id: <20200716145031.771476-1-cohuck@redhat.com>

docs/system/s390x/vfio-ccw.rst

@@ -29,7 +29,7 @@ automatically, use
 
    [root@host ~]# driverctl -b css set-override 0.0.0313 vfio_ccw
    [root@host ~]# mdevctl define -u 7e270a25-e163-4922-af60-757fc8ed48c6 \
-                  -p 0.0.0313 -t vfio-ccw_io -a
+                  -p 0.0.0313 -t vfio_ccw-io -a
 
 If using ``mdevctl`` is not possible or wanted, follow the manual procedure
 below.