use get_function method rather than accessing a (renamed) field

Author: OCHyams

cross-project-tests/debuginfo-tests/dexter/dex/debugger/DebuggerControllers/ConditionalController.py

@@ -197,7 +197,7 @@ def _build_bp_ranges(self):
                 self._bp_ranges.append(bpr)
         if "DexStepFunction" in commands:
             for c in commands["DexStepFunction"]:
-                bpr = BreakpointRange.step_function(c.expression, c.path, c.hit_count)
+                bpr = BreakpointRange.step_function(c.get_function(), c.path, c.hit_count)
                 self._bp_ranges.append(bpr)
 
     def _set_leading_bps(self):