Found during research of {T77124}. In `build_driver_data` an identical
RNA_path is resolved twice. In stead of resolving it twice this patch
will construct the `property_exit_key` based on the resolution of
`property_entry_key`.
This change isn't noticeable for users. Just a cleanup as it isn't
needed to do the same logic twice.
Reviewed By: Sergey Sharybin
Differential Revision: https://developer.blender.org/D7872
0749cff957