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/structs.h b/src/structs.h
index fb56e01..242c4b7 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -3698,7 +3698,7 @@
 
     int		w_redr_type;	    // type of redraw to be performed on win
     int		w_upd_rows;	    // number of window lines to update when
-				    // w_redr_type is REDRAW_TOP
+				    // w_redr_type is UPD_REDRAW_TOP
     linenr_T	w_redraw_top;	    // when != 0: first line needing redraw
     linenr_T	w_redraw_bot;	    // when != 0: last line needing redraw
     int		w_redr_status;	    // if TRUE status line must be redrawn