Servo: minor fixups

[toru-kuga]

Description

Some fix, that seemed wrong from the code context.
The fix are minor and not serious.
-fixed a wrapper calling wrong member, though normally returning same value
-suppressed a wrong ROS_WARN message

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[welcome]

Thanks for helping in improving MoveIt and open source robotics!

[codecov]

Codecov Report

Merging #2759 (ed91125) into master (83c82e3) will decrease coverage by 0.07%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #2759      +/-   ##
==========================================
- Coverage   60.49%   60.43%   -0.06%     
==========================================
  Files         404      404              
  Lines       29670    29670              
==========================================
- Hits        17947    17927      -20     
- Misses      11723    11743      +20     

Impacted Files	Coverage Δ
moveit_ros/moveit_servo/src/servo.cpp	68.71% <0.00%> (ø)
moveit_ros/moveit_servo/src/servo_calcs.cpp	63.70% <100.00%> (-0.20%)	⬇️
.../ompl_interface/src/detail/constrained_sampler.cpp	43.25% <0.00%> (-16.21%)	⬇️
...e/src/parameterization/model_based_state_space.cpp	68.31% <0.00%> (-2.81%)	⬇️
moveit_core/robot_model/src/joint_model_group.cpp	63.06% <0.00%> (-1.94%)	⬇️
...meterization/work_space/pose_model_state_space.cpp	81.42% <0.00%> (-1.92%)	⬇️
...e/collision_detection_fcl/src/collision_common.cpp	78.18% <0.00%> (+0.26%)	⬆️

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[welcome]

Congrats on getting your first MoveIt pull request merged and improving open source robotics!