patch 9.0.1743: Parameter of gui_gtk:gui_mch_browse incorrectly marked as UNUSED

Problem:    Parameter of gui_gtk:gui_mch_browse incorrectly marked as
            UNUSED.
Solution:   Remove UNUSED flag.

closes: #12841

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Doug Kearns <dougkearns@gmail.com>
diff --git a/src/gui_gtk.c b/src/gui_gtk.c
index 6dbaf24..69a9cae 100644
--- a/src/gui_gtk.c
+++ b/src/gui_gtk.c
@@ -1239,10 +1239,10 @@
  * dflt				default name
  * ext				not used (extension added)
  * initdir			initial directory, NULL for current dir
- * filter			not used (file name filter)
+ * filter			file name filter
  */
     char_u *
-gui_mch_browse(int saving UNUSED,
+gui_mch_browse(int saving,
 	       char_u *title,
 	       char_u *dflt,
 	       char_u *ext UNUSED,