crypto: sun8i-ss - Fix memory leak of pad

It appears there are several failure return paths that don't seem
to be free'ing pad. Fix these.

Addresses-Coverity: ("Resource leak")
Fixes: d9b45418 ("crypto: sun8i-ss - support hash algorithms")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>