patch 8.1.0113: compiler warning for unused variable

Problem:    Compiler warning for unused variable. (Yegappan Lakshmanan)
Solution:   Add UNUSED. (Christian Brabandt)
diff --git a/src/screen.c b/src/screen.c
index b5b68e4..eac50c5 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -6874,7 +6874,7 @@
  * displayed.
  */
     static void
-win_redr_status(win_T *wp, int ignore_pum)
+win_redr_status(win_T *wp, int ignore_pum UNUSED)
 {
     int		row;
     char_u	*p;