Fix dndk-gcm decrypt benchmark input

Author: script3r

benches/src/dndk-gcm.rs

@@ -24,7 +24,9 @@ fn bench(c: &mut Benchmarker) {
         });
         group.bench_function(BenchmarkId::new("decrypt-256", size), |b| {
             let cipher = DndkGcm::new(&Default::default());
-            b.iter(|| cipher.decrypt(&Default::default(), &*buf))
+            let nonce = Default::default();
+            let ciphertext = cipher.encrypt(&nonce, &*buf).unwrap();
+            b.iter(|| cipher.decrypt(&nonce, ciphertext.as_ref()))
         });
     }