message: fix gkernel Doxygen documentation
diff: @@ -719,7 +719,7 @@ namespace gapi {
  * @{
  */
  /**
  - * @brief cv::use_only() is a special combinator which hints G-API to use only
  + * @brief cv::gapi::use_only() is a special combinator which hints G-API to use only
  * kernels specified in cv::GComputation::compile() (and not to extend kernels available by
  * default with that package).
  */
  