[relay][frontend][pytorch]Fix a bug in the _get_pytorch_value_type function (#14421)

* Fix a bug in the _get_pytorch_value_type function

* Fix lint

Author: liwangshengya

python/tvm/relay/frontend/pytorch.py

@@ -4493,7 +4493,7 @@ def _get_pytorch_value_type(typ, default_dtype="float32"):
         return "ListType"
     elif kind in ["IntType", "FloatType", "BoolType", "StringType", "OptionalType"]:
         pt_dtype = str(typ).lower()
-        dtype = pt_dtype if pt_dtype == "OptionalType" else _convert_data_type(pt_dtype)
+        dtype = pt_dtype if kind == "OptionalType" else _convert_data_type(pt_dtype)
         return dtype
     else:
         return "UnsupportedType"