commit 6e8d8ecf upstream.

This patch adds an exception to the key check so that cipher_null
users may continue to use algif_skcipher without setting a key.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
[bwh: Backported to 3.2: use crypto_ablkcipher_has_setkey()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>