Kernel-doc: Convention: Use a "Return" section to describe return values

Non-void functions should describe their return values in their kernel-doc
comments. Currently, some don't, others do in various forms. For example:
   * Return the result.
   * Return: The result.
   * Returns the result.
   * Returns: the result.
   * Return Value: The result.
   * @return: the result.
   * This function returns the result.
   * It will return the result.

Defining a convention would improve consistency of kernel-doc comments. It
would also help scripts/kernel-doc identify the text describing the return
value of a function. Thus allowing additional checks on the comments, and
suitable highlighting in the generated docs (man pages, html, etc).

So, as a convention, use a section named "Return" to describe the return
value of a function.

Signed-off-by: Yacine Belkadi <yacine.belkadi.1@gmail.com>
Signed-off-by: Rob Landley <rob@landley.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>