* doxygen: remove @return command if function return void
When doxygen is upgraded to v1.9.8 (on ubuntu 24.04), doxygen
reports: "doxygen error: found documented return type for xxx
that does not return anything" for those functions which return
void but declare "@return" in doxygen comment.
Solution: remove "@return" for those cases, and update
guide document for how to write doxgen comment for functions.
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
* doxygen: fixed a minor typo for uart doc
This error is found when building with doxygen 1.9.8, but not
detecetd on 1.9.1.
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
273185b45a