crypto: chelsio - don't leak pointers to authenc keys

In chcr_authenc_setkey and chcr_aead_digest_null_setkey we save
pointers to the authenc keys in local variables of type
struct crypto_authenc_keys and we don't zeroize them after use.
Fix this and don't leak pointers to the authenc keys.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>