Fix an import after previous refactor (pytorch#471)

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Author: jerryzh168

torchao/dtypes/affine_quantized_tensor.py

@@ -509,9 +509,10 @@ def __torch_dispatch__(cls, func, types, args, kwargs):
     def get_plain(self):
         from torchao.quantization.quant_primitives import (
             ZeroPointDomain,
-            unpack_tinygemm_scales_and_zeros,
             quantize_affine,
         )
+        from torchao.quantization.utils import unpack_tinygemm_scales_and_zeros
+
         cur_shape = self.shape
         assert len(cur_shape) == 4
         inner_k_tiles = cur_shape[-1] * 2