[diff_drive_controller] Made odom topic name relative as it was in ROS1. (ros-controls#343)

Author: tonybaltovski

diff_drive_controller/src/diff_drive_controller.cpp

@@ -33,7 +33,7 @@ namespace
 constexpr auto DEFAULT_COMMAND_TOPIC = "~/cmd_vel";
 constexpr auto DEFAULT_COMMAND_UNSTAMPED_TOPIC = "~/cmd_vel_unstamped";
 constexpr auto DEFAULT_COMMAND_OUT_TOPIC = "~/cmd_vel_out";
-constexpr auto DEFAULT_ODOMETRY_TOPIC = "/odom";
+constexpr auto DEFAULT_ODOMETRY_TOPIC = "~/odom";
 constexpr auto DEFAULT_TRANSFORM_TOPIC = "/tf";
 }  // namespace