Fix whitespace in example

Line up the second line in the way that the example purports to be
showing.
Signed-off-by: NMatthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/doc-guide/kernel-doc.rst

@@ -154,7 +154,7 @@ The ``@argument:`` descriptions may span multiple lines.
    the previous line, e. g.::
 
       * @argument: some long description
-      *       that continues on next lines
+      *            that continues on next lines
 
    or::