crypto: sun4i-ss - use GENMASK to generate masks

Use the GENMASK helper instead of custom calculations to generate masks,
It also helps the readability.
Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Acked-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

@@ -384,12 +384,15 @@ static int sun4i_hash(struct ahash_request *areq)
 			writesl(ss->base + SS_RXFIFO, op->buf, nwait);
 			op->byte_count += 4 * nwait;
 		}
+
 		nbw = op->len - 4 * nwait;
+		if (nbw) {
 			wb = *(u32 *)(op->buf + nwait * 4);
-		wb &= (0xFFFFFFFF >> (4 - nbw) * 8);
+			wb &= GENMASK((nbw * 8) - 1, 0);
 
 			op->byte_count += nbw;
 		}
+	}
 
 	/* write the remaining bytes of the nbw buffer */
 	wb |= ((1 << 7) << (nbw * 8));