rkanoid: invert accel sensor direction

this one got reversed in recent c-firmware revisions.

rkanoid/src/main.rs

@@ -212,9 +212,9 @@ fn game(level: u16, mut score: u32) -> GameResult {
             paddle += PADDLE_SPEED;
         }
         if accel_x < 0 {
-            paddle = paddle.saturating_sub(-accel_x as u32);
+            paddle += -accel_x as u32;
         } else if accel_x > 0 {
-            paddle += accel_x as u32;
+            paddle = paddle.saturating_sub(accel_x as u32);
         }
         paddle = paddle
             .max(paddle_size)