Documentation: fix vfio-ccw doc

commit 4c4cbbaa upstream.

*Really* mark the literal block as such.

Fixes: 127e6217 ("vfio-ccw: Update documentation for csch/hsch")
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>