crypto: ccree - defer larval_digest_addr init until needed

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>