crypto: sun8i-ss - handle zero sized sg

sun8i-ss does not handle well the possible zero sized sg.

Fixes: d9b45418 ("crypto: sun8i-ss - support hash algorithms")
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/allwinner/sun8i-ss/sun8i-ss-hash.c

@@ -380,13 +380,21 @@ int sun8i_ss_hash_run(struct crypto_engine *engine, void *breq)
 	}
 
 	len = areq->nbytes;
-	for_each_sg(areq->src, sg, nr_sgs, i) {
+	sg = areq->src;
+	i = 0;
+	while (len > 0 && sg) {
+		if (sg_dma_len(sg) == 0) {
+			sg = sg_next(sg);
+			continue;
+		}
 		rctx->t_src[i].addr = sg_dma_address(sg);
 		todo = min(len, sg_dma_len(sg));
 		rctx->t_src[i].len = todo / 4;
 		len -= todo;
 		rctx->t_dst[i].addr = addr_res;
 		rctx->t_dst[i].len = digestsize / 4;
+		sg = sg_next(sg);
+		i++;
 	}
 	if (len > 0) {
 		dev_err(ss->dev, "remaining len %d\n", len);