While the larval digest addresses are not always used in
cc_get_plain_hmac_key() and cc_hash_digest(), they are always
calculated.

Defer their calculations to the points where needed.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>