crypto: aegis128 - wipe plaintext and tag if decryption fails

The AEGIS spec mentions explicitly that the security guarantees hold
only if the resulting plaintext and tag of a failed decryption are
withheld. So ensure that we abide by this.

While at it, drop the unused struct aead_request *req parameter from
crypto_aegis128_process_crypt().

Reviewed-by: Ondrej Mosnacek <omosnacek@gmail.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>