s390/zcrypt: Use kvcalloc() instead of kvmalloc_array()

sparse warns about a large memset() call within
zcrypt_device_status_mask_ext():

drivers/s390/crypto/zcrypt_api.c:1303:15: warning: memset with byte count of 262144

Get rid of this warning by making sure that all callers of this function
allocate memory with __GFP_ZERO, which zeroes memory already at allocation
time, which again allows to remove the memset() call.

Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>