[Fix] Fix the wrong index of coor in middle_encoder.pillar_scatter.forward_single (#1280)

* fix the wrong index of coor in middle_encoder.pillar_scatter.forward_single

* make it consistent with forward_batch
Co-authored-by: Tai-Wang <tab_wang@outlook.com>

mmdet3d/models/middle_encoders/pillar_scatter.py

@@ -50,14 +50,14 @@ class PointPillarsScatter(nn.Module):
             dtype=voxel_features.dtype,
             device=voxel_features.device)
 
-        indices = coors[:, 1] * self.nx + coors[:, 2]
+        indices = coors[:, 2] * self.nx + coors[:, 3]
         indices = indices.long()
         voxels = voxel_features.t()
         # Now scatter the blob back to the canvas.
         canvas[:, indices] = voxels
         # Undo the column stacking to final 4-dim tensor
         canvas = canvas.view(1, self.in_channels, self.ny, self.nx)
-        return [canvas]
+        return canvas
 
     def forward_batch(self, voxel_features, coors, batch_size):
         """Scatter features of single sample.