smbencrypt() points a scatterlist to the stack, which is breaks if
CONFIG_VMAP_STACK=y.

Fix it by switching to crypto_cipher_encrypt_one().  The new code
should be considerably faster as an added benefit.

This code is nearly identical to some code that Eric Biggers
suggested.

Cc: stable@vger.kernel.org # 4.9 only
Reported-by: NEric Biggers <ebiggers3@gmail.com>
Signed-off-by: NAndy Lutomirski <luto@kernel.org>
Acked-by: NJeff Layton <jlayton@redhat.com>
Signed-off-by: NSteve French <smfrench@gmail.com>