Fix arguments in CTC decoding script (pytorch#2315)

Summary:
Some arguments in `ArgumentParser` are not used in the `lexicon_decoder`. Fix them to use the ones in the parser.

Pull Request resolved: pytorch#2315

Reviewed By: carolineechen

Differential Revision: D35357678

Pulled By: nateanl

fbshipit-source-id: 4e70418cf03708b82bc158cafd9999a80ad08f92

examples/asr/librispeech_ctc_decoder/inference.py

@@ -35,14 +35,14 @@ def run_inference(args):
         lexicon=lexicon_file,
         tokens=tokens,
         lm=kenlm_file,
-        nbest=1,
-        beam_size=1500,
-        beam_size_token=None,
-        beam_threshold=50,
+        nbest=args.nbest,
+        beam_size=args.beam_size,
+        beam_size_token=args.beam_size_token,
+        beam_threshold=args.beam_threshold,
         lm_weight=args.lm_weight,
         word_score=args.word_score,
-        unk_score=float("-inf"),
-        sil_score=0,
+        unk_score=args.unk_score,
+        sil_score=args.sil_score,
         log_add=False,
     )