Fix normal orientation loss (#1298)

Co-authored-by: Abhik Ahuja <ahujaabhik@berkeley.edu>

nerfstudio/model_components/losses.py

@@ -193,7 +193,7 @@ def orientation_loss(
     """
     w = weights
     n = normals
-    v = viewdirs
+    v = viewdirs * -1
     n_dot_v = (n * v[..., None, :]).sum(axis=-1)
     return (w[..., 0] * torch.fmin(torch.zeros_like(n_dot_v), n_dot_v) ** 2).sum(dim=-1)