forward fix for D68269174

Differential Revision: D68451854

Pull Request resolved: pytorch#7797

Author: Gasoonjia

backends/arm/arm_backend.py

@@ -50,6 +50,7 @@ def __init__(self):
         self.output_format = None
         self.path_for_intermediates = None
         self.tosa_version = None
+        self.tosa_spec = None
         self.input_order = None
 
     def ethosu_compile_spec(