crypto: sun8i-ss - Fix error codes for dma_mapping_error()

If there is a dma_mapping_error() then return negative error codes.
Currently this code returns success.

Fixes: 801b7d57 ("crypto: sun8i-ss - add hmac(sha1)")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.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>