crypto: x86/cast5-avx - fix ECB encryption when long sg follows short one

With ecb-cast5-avx, if a 128+ byte scatterlist element followed a
shorter one, then the algorithm accidentally encrypted/decrypted only 8
bytes instead of the expected 128 bytes.  Fix it by setting the
encryption/decryption 'fn' correctly.

Fixes: c12ab20b ("crypto: cast5/avx - avoid using temporary stack buffers")
Cc: <stable@vger.kernel.org> # v3.8+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>