s390/zcrypt: Fix ZCRYPT_PERDEV_REQCNT ioctl

reqcnt is an u32 pointer but we do copy sizeof(reqcnt) which is the
size of the pointer. This means we only copy 8 byte. Let us copy
the full monty.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Harald Freudenberger <freude@linux.ibm.com>
Cc: stable@vger.kernel.org
Fixes: af4a7227

 ("s390/zcrypt: Support up to 256 crypto adapters.")
Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>