s390/zcrypt: Fix invalid domain handling during ap module unload

Added domain checking to prevent reset failures caused by invalid
domains.
Corrected removal sequence of bus attributes and device.

Reviewed-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Ingo Tuchscherer <ingo.tuchscherer@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>