fix script read_mat (#3852)

Author: Wonkyum

egs/aishell/s10/chain/feat_dataset.py

@@ -15,7 +15,6 @@
 import kaldi_pybind.nnet3 as nnet3
 import kaldi
 
-from common import read_mat
 from common import splice_feats
 from model import get_chain_model
 
@@ -110,7 +109,7 @@ def __call__(self, batch):
         for b in batch:
             key, rxfilename = b
             key_list.append(key)
-            feat = read_mat(rxfilename)
+            feat = kaldi.read_mat(rxfilename).numpy()
             feat_len = feat.shape[0]
             output_len = (feat_len + self.frame_subsampling_factor -
                           1) // self.frame_subsampling_factor