crypto: marvell - Use IPAD/OPAD constant

This patch simply replace all occurrence of HMAC IPAD/OPAD value by their
define.

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>