Added hook to change battery voltage.

Change-Id: Ide009e808fb6ba21d0463166e71cb5b19f300fe0
diff --git a/aos/common/controls/control_loop_test.cc b/aos/common/controls/control_loop_test.cc
index ecaafab..44af93a 100644
--- a/aos/common/controls/control_loop_test.cc
+++ b/aos/common/controls/control_loop_test.cc
@@ -51,8 +51,8 @@
     new_state->voltage_3v3 = 3.3;
     new_state->voltage_5v = 5.0;
 
-    new_state->voltage_roborio_in = 12.4;
-    new_state->voltage_battery = 12.4;
+    new_state->voltage_roborio_in = battery_voltage_;
+    new_state->voltage_battery = battery_voltage_;
 
     new_state.Send();
   }