crypto: x86/aegis256 - Fix wrong key buffer size

AEGIS-256 key is two blocks, not one.

Fixes: 1d373d4e ("crypto: x86 - Add optimized AEGIS implementations")
Reported-by: Eric Biggers <ebiggers3@gmail.com>
Signed-off-by: Ondrej Mosnacek <omosnacek@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>