Fix angular velocity direction of diff_drive_controller odometry (backport #281)

[mergify]

This is an automatic backport of pull request #281 done by Mergify.
Cherry-pick of 9a8be06 has failed:

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	both modified:   diff_drive_controller/src/odometry.cpp

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[bmagyar]

This backport doesn't apply to Foxy as the bug was not present there in the first place