Fix download link for raft_small (#5078)

Author: NicolasHug

references/optical_flow/README.md

@@ -62,4 +62,4 @@ You can also evaluate on Kitti train:
 ```
 torchrun --nproc_per_node 1 --nnodes 1 train.py --val-dataset kitti --batch-size 1 --dataset-root $dataset_root --model raft_large --pretrained
 Kitti val epe: 4.7968	1px: 0.6388	3px: 0.8197	5px: 0.8661	per_image_epe: 4.5118	f1: 16.0679
-```
+```

torchvision/prototype/models/optical_flow/raft.py

@@ -97,11 +97,11 @@ class Raft_Small_Weights(WeightsEnum):
     )
     C_T_V2 = Weights(
         # Chairs + Things
-        url="https://github.com/pytorch/vision/tree/main/references/optical_flow",
+        url="https://download.pytorch.org/models/raft_small_C_T_V2-01064c6d.pth",
         transforms=RaftEval,
         meta={
             **_COMMON_META,
-            "recipe": "https://github.com/princeton-vl/RAFT",
+            "recipe": "https://github.com/pytorch/vision/tree/main/references/optical_flow",
             "sintel_train_cleanpass_epe": 1.9901,
             "sintel_train_finalpass_epe": 3.2831,
             "kitti_train_per_image_epe": 7.5978,