[int8 woq] make the scale type the same as input for bf16 autocast (#534)

Author: Valentine233

torchao/dtypes/affine_quantized_tensor.py

@@ -795,17 +795,15 @@ def _quantized_linear_op(input_tensor, weight_qtensor, bias):
             w_vals_int8_t = weight_qtensor.layout_tensor.int_data.t()
             scale = weight_qtensor.layout_tensor.scale
             orig_dtype = input_tensor.dtype
-            y = (
-                torch.mm(
+            m = torch.mm(
                     input_tensor.reshape(-1, input_tensor.shape[-1]),
                     w_vals_int8_t.to(input_tensor.dtype),
                 )
-                * scale
-            )
+            y = m * scale.to(m.dtype)
             y = y.reshape(*input_tensor.shape[:-1], y.shape[-1])
             if bias is not None:
-                y += bias
-            return y.to(orig_dtype)
+                y += bias.to(m.dtype)
+            return y
 
             # is_cpu and is_mps only, some issue with is_contiguous() currently
             # return torch.ops.aten._weight_int8pack_mm(input_tensor.contiguous(), w_vals_int8_t, weight_qtensor.layout_tensor.scale)