s390/zcrypt: Explicitly use a card variable in _zcrypt_send_cprb

s390/zcrypt: Explicitly use a card variable in _zcrypt_send_cprb

Use an explicit variable "card" for the card addressing in
function _zcrypt_send_cprb instead of the confusing field
"user_defined" from the ica_xcRB struct. This makes the code
somewhat cleaner and easier to understand.

Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>