Put a plant inside the loop and moved A,B,etc there.

Change-Id: I9cb3a1a16bd0ccda0c9287514577b3c3861bc42f
diff --git a/frc971/control_loops/drivetrain/drivetrain.cc b/frc971/control_loops/drivetrain/drivetrain.cc
index 6a2822b..2e680a3 100644
--- a/frc971/control_loops/drivetrain/drivetrain.cc
+++ b/frc971/control_loops/drivetrain/drivetrain.cc
@@ -112,14 +112,14 @@
       break;
   }
 
-  kf_.set_controller_index(ControllerIndexFromGears());
+  kf_.set_index(ControllerIndexFromGears());
   {
     GearLogging gear_logging;
     gear_logging.left_state = static_cast<uint32_t>(left_gear_);
     gear_logging.right_state = static_cast<uint32_t>(right_gear_);
     gear_logging.left_loop_high = MaybeHigh(left_gear_);
     gear_logging.right_loop_high = MaybeHigh(right_gear_);
-    gear_logging.controller_index = kf_.controller_index();
+    gear_logging.controller_index = kf_.index();
     LOG_STRUCT(DEBUG, "state", gear_logging);
   }
   const bool is_latest_imu_values = ::frc971::imu_values.FetchLatest();