RCC development guide code syntax update

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What this MR does / why we need it:

MR fixes minor typo in OpenCPI RCC Development Guide. An example RCC element is ended twice in the XML.

Steps to complete before submitting MR:

• I have read Contribution guidelines

• My branch is up to date with develop. If it is not, then I have ensured my work does not conflict with other work

• (REVIEWER ONLY) I have thoroughly gone through the above steps to ensure that they have been followed

Which issue(s) this MR closes

Closes #3146 (closed)