patch 9.0.0206: redraw flags are not named specifically

Problem:    Redraw flags are not named specifically.
Solution:   Prefix "UPD_" to the flags, for UPDate_screen().
diff --git a/src/getchar.c b/src/getchar.c
index f3dbe4a..c7601ef 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -2098,7 +2098,7 @@
 
     // redraw the screen after getchar()
     if (p_ch == 0)
-	update_screen(CLEAR);
+	update_screen(UPD_CLEAR);
 
     set_vim_var_nr(VV_MOUSE_WIN, 0);
     set_vim_var_nr(VV_MOUSE_WINID, 0);