HS: Fix hs section set and display.

src/Model/HydraulicStructures/HydraulicStructures.py

@@ -355,13 +355,15 @@ class HydraulicStructure(SQLSubModel):
     def input_rk(self):
         if self._input_section is None:
             return None
-        return self._input_section.rk
+
+        return self._input_section
 
     @property
     def output_rk(self):
         if self._output_section is None:
             return None
-        return self._output_section.rk
+
+        return self._output_section
 
     @property
     def input_section(self):