s390/zcrypt: fix broken zcrypt_send_cprb in-kernel api function

With the new multi zcrypt device node support there came
in a code rework which broke the in-kernel api function
zcrypt_send_cprb(). This function is used by the pkey kernel
module and as an effect, transforming a secure key into a
protected key did not work any more.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>