Fixing initialization of dictionary in dataclass (#3749)

Summary:
Pull Request resolved: #3749

same as title

Reviewed By: satymish

Differential Revision: D61133788

fbshipit-source-id: 5761e6347365f7701ee0600a9d895b8bd1f0a6b8

Author: kuarora

benchs/bench_fw/benchmark_io.py

@@ -46,7 +46,10 @@ def merge_rcq_itq(
 @dataclass
 class BenchmarkIO:
     path: str
-    cached_ds: Dict[Any, Any] = {}
+
+    def __init__(self, path: str):
+        self.path = path
+        self.cached_ds: Dict[Any, Any] = {}
 
     def clone(self):
         return BenchmarkIO(path=self.path)