s390/zcrypt: fix wrong offset index for APKA master key valid state

Tests showed a mismatch between what the CCA tool reports about
the APKA master key state and what's displayed by the zcrypt dd
in sysfs. After some investigation, we found out that the
documentation which was the source for the zcrypt dd implementation
lacks the listing of 3 fields. So this patch now moves the
evaluation of the APKA master key state to the correct offset.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>