s390/zcrypt: fixed domain scanning problem (again)

Older machines with more then 16 domains need a special check before
PQAP instructions can be processed. With commit 5bc334bf

 this
check was reverted by accident. This patch re-establishes the additional
code needed for checking the extended domains for older machines.

Signed-off-by: Ingo Tuchscherer <ingo.tuchscherer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>