pc-bios/s390-ccw/virtio: Read device config after feature negotiation

pc-bios/s390-ccw/virtio: Read device config after feature negotiation

Feature negotiation should be done first, since some fields in the
config area can depend on the negotiated features and thus should
rather be read afterwards.

While we're at it, also adjust the error message here a little bit
(the code is nowadays used for non-block virtio devices, too).

Message-Id: <20220704111903.62400-8-thuth@redhat.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>