s390/pkey: fix memory leak within _copy_apqns_from_user()

commit f9cac4fd upstream.

Fixes: f2bbc96e ("s390/pkey: add CCA AES cipher key support")
Reported-by: Markus Elfring <Markus.Elfring@web.de>
Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>