crypto: rockchip - add fallback for ahash

Adds a fallback for all case hardware cannot handle.

Fixes: ce0183cb

 ("crypto: rockchip - switch to skcipher API")
Reviewed-by: John Keeping <john@metanate.com>
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>