doc:it_IT:doc-guide: fix reference to foobar

Replicate the following patch into italian translation

1bb37a35  doc-guide:kernel-doc.rst: Reference to foobar
Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/translations/it_IT/doc-guide/kernel-doc.rst

@@ -107,7 +107,7 @@ macro simil-funzioni è il seguente::
    * Context: Describes whether the function can sleep, what locks it takes,
    *          releases, or expects to be held. It can extend over multiple
    *          lines.
-   * Return: Describe the return value of foobar.
+   * Return: Describe the return value of function_name.
    *
    * The return value description can also have multiple paragraphs, and should
    * be placed at the end of the comment block.