fix eval-related doc errors (#2183)

Signed-off-by: Steven Palma <imstevenpmwork@ieee.org>
Co-authored-by: Steven Palma <imstevenpmwork@ieee.org>

src/lerobot/scripts/lerobot_eval.py

@@ -27,7 +27,7 @@ lerobot-eval \
     --eval.batch_size=10 \
     --eval.n_episodes=10 \
     --use_amp=false \
-    --device=cuda
+    --policy.device=cuda
 ```
 
 OR, you want to evaluate a model checkpoint from the LeRobot training script for 10 episodes.
@@ -38,7 +38,7 @@ lerobot-eval \
     --eval.batch_size=10 \
     --eval.n_episodes=10 \
     --use_amp=false \
-    --device=cuda
+    --policy.device=cuda
 ```
 
 Note that in both examples, the repo/folder should contain at least `config.json` and `model.safetensors` files.