widget: silence g-i scanner warning

The parameter should be named the same in the definition and the
declararion.

https://bugzilla.gnome.org/show_bug.cgi?id=677127

gtk/gtkwidget.c

@@ -1689,7 +1689,7 @@ gtk_widget_class_init (GtkWidgetClass *klass)
   /**
    * GtkWidget::child-notify:
    * @widget: the object which received the signal
-   * @pspec: the #GParamSpec of the changed child property
+   * @child_property: the #GParamSpec of the changed child property
    *
    * The ::child-notify signal is emitted for each
    * <link linkend="child-properties">child property</link>  that has

gtk/gtkwidget.h

@@ -229,7 +229,7 @@ struct _GtkWidgetClass
   void (* grab_notify)         (GtkWidget        *widget,
 				gboolean          was_grabbed);
   void (* child_notify)        (GtkWidget	 *widget,
-				GParamSpec       *pspec);
+				GParamSpec       *child_property);
   gboolean (* draw)	       (GtkWidget	 *widget,
                                 cairo_t          *cr);