s390x/css: Fix concurrent sense.

Fix an off-by-one error when indicating availablity of concurrent
sense data.

Cc: qemu-stable@nongnu.org
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
virtio-ccw: Fix unsetting of indicators.

Interpretation of the ccws to register (configuration) indicators contained
a thinko: We want to disallow reading from 0, but setting the indicator
pointer to 0 is fine.

Let's fix the handling for CCW_CMD_SET{,_CONF}_IND.

Cc: qemu-stable@nongnu.org
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>