s390/css: stop stsch loop after cc 3

s390/css: stop stsch loop after cc 3

Receiving cc=3 from store subchannel means 2 things:
* the subchannel is not provided
* there are no further subchannels in this subchannel set

With this patch we abort the store subchannel loop after cc=3 (or an
exception) and clear the subsequent bits in the subchannel id set.

Reported-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Acked-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>