Fix position ids logic instantiation of idefics vision part (#1064)

Problem and fix is described here:
https://huggingface.co/HuggingFaceM4/idefics-9b/discussions/9



---------
Co-authored-by: Nicolas Patry <patry.nicolas@protonmail.com>

server/text_generation_server/models/custom_modeling/idefics_vision.py

@@ -88,12 +88,10 @@ class IdeficsVisionEmbeddings(nn.Module):
 
         self.num_patches = (self.image_size // self.patch_size) ** 2
         self.num_positions = self.num_patches + 1
-        # self.position_embedding = nn.Embedding(self.num_positions, self.embed_dim)
         self.position_embedding = TensorParallelEmbedding(
             prefix="model.vision_model.embeddings.position_embedding", weights=weights
         )
-        # self.register_buffer("position_ids", torch.arange(self.num_positions).expand((1, -1)), persistent=False)
-        self.position_ids = weights.get_tensor(f"{prefix}.position_ids")
+        self.position_ids = torch.arange(self.num_positions).expand((1, -1)).to(device=weights.device)
 
     def forward(self, pixel_values: torch.FloatTensor) -> torch.Tensor:
         batch_size = pixel_values.shape[0]