s390/zcrypt: fix kmalloc 256k failure

s390/zcrypt: fix kmalloc 256k failure

commit b6186d7fb53349efd274263a45f0b08749ccaa2d upstream.

Tests showed that under stress conditions the kernel may
temporary fail to allocate 256k with kmalloc. However,
this fix reworks the related code in the cca_findcard2()
function to use kvmalloc instead.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Ingo Franzki <ifranzki@linux.ibm.com>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>