fix a type mismatch in NAT quantization run

Summary:
Fix a type mismatch which was found after patching NAT on top of quantization.
Ning suggested this fix. Need to further understand: why this only appears after patching quantization diff?

Reviewed By: kahne, jhcross

Differential Revision: D18147726

fbshipit-source-id: a51becc9ad58a637a0180074eaa2b46990ab9f84

fairseq/models/model_utils.py

@@ -108,7 +108,7 @@ def fill_tensors(x, mask, y, padding_idx: int):
         x = expand_2d_or_3d_tensor(x, y.size(1), padding_idx)
         x[mask] = y
     elif x.size(1) > y.size(1):
-        x[mask] = torch.tensor(padding_idx)
+        x[mask] = torch.tensor(padding_idx).type_as(x)
         if x.dim() == 2:
             x[mask, :y.size(1)] = y
         else: