crypto: sun4i-ss - Fix invalid calculation of hash end

When nbytes < 4, end is wronlgy set to a negative value which, due to
uint, is then interpreted to a large value leading to a deadlock in the
following code.

This patch fix this problem.

Fixes: 6298e948 ("crypto: sunxi-ss - Add Allwinner Security System crypto accelerator")
Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/sunxi-ss/sun4i-ss-hash.c

@@ -240,7 +240,10 @@ static int sun4i_hash(struct ahash_request *areq)
 		}
 	} else {
 		/* Since we have the flag final, we can go up to modulo 4 */
-		end = ((areq->nbytes + op->len) / 4) * 4 - op->len;
+		if (areq->nbytes < 4)
+			end = 0;
+		else
+			end = ((areq->nbytes + op->len) / 4) * 4 - op->len;
 	}
 
 	/* TODO if SGlen % 4 and !op->len then DMA */