device: do not attach finalizer to non-returned object

Before, the code attached a finalizer to an object that wasn't returned,
resulting in immediate garbage collection. Instead return the actual
pointer.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

device/pools_test.go

@@ -80,4 +80,4 @@ func BenchmarkWaitPool(b *testing.B) {
 		}()
 	}
 	wg.Wait()
-}
+}