virtio-ccw: range check in READ_VQ_CONF

Processing for READ_VQ_CONF needs to check whether the requested queue
value is actually in the supported range and post a channel program
check if not.

Cc: qemu-stable@nongnu.org
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>