unittest/test_files.TransparentEF_Test: Actually test encoder

In the test_encode_file() method, we should actually test the encoder,
and not the decoder.  I suppose this was a copy+paste mistake at some
point?  In the LinearFixedEF_Test.test_encoder_record we were already
testing the encoder. Just TransparentEF_Test got it wrong...

Change-Id: Id23305a78ab9acd2e006f2b26b72408795844d23

tests/unittests/test_files.py

@@ -256,8 +256,8 @@ class TransparentEF_Test(unittest.TestCase):
                         encoded = t[0]
                         decoded = t[1]
                         logging.debug("Testing encode of %s", name)
-                        re_dec = inst.decode_hex(encoded)
-                        self.assertEqual(decoded, re_dec)
+                        re_enc = inst.encode_hex(decoded)
+                        self.assertEqual(encoded, re_enc)
 
     def test_de_encode_file(self):
         """Test the decoder and encoder for a transparent EF.  Performs first a decoder