doc-guide: kernel-doc: fix example for nested_foobar struct

There's a missing */ at the end of Kernel docs example.
Even adding it, it will still produce 3 warnings:

	example:33: warning: Function parameter or member 'bar' not described in 'nested_foobar'
	example:33: warning: Function parameter or member 'bar.st1' not described in 'nested_foobar'
	example:33: warning: Function parameter or member 'bar.st2' not described in 'nested_foobar'

So, make the example more complete and add the missing end
of comment there.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/doc-guide/kernel-doc.rst

@@ -250,10 +250,14 @@ It is possible to document nested structs and unions, like::
        * @memb2: second member of anonymous union/anonymous struct
        * @memb3: third member of anonymous union/anonymous struct
        * @memb4: fourth member of anonymous union/anonymous struct
+       * @bar: non-anonymous union
+       * @bar.st1: struct st1 inside @bar
+       * @bar.st2: struct st2 inside @bar
        * @bar.st1.memb1: first member of struct st1 on union bar
        * @bar.st1.memb2: second member of struct st1 on union bar
        * @bar.st2.memb1: first member of struct st2 on union bar
        * @bar.st2.memb2: second member of struct st2 on union bar
+       */
       struct nested_foobar {
         /* Anonymous union/struct*/
         union {