tools/xentop : fix vwprintw -Werror=deprecated-declarations warning

gcc-8.1 complains:

| xentop.c: In function 'print':
| xentop.c:304:4: error: 'vwprintw' is deprecated [-Werror=deprecated-declarations]
|     vwprintw(stdscr, (curses_str_t)fmt, args);
|     ^~~~~~~~

vw_printw is the non-deprecated alternative.

Signed-off-by: Christopher Clark <christopher.clark6@baesystems.com>
diff --git a/tools/xenstat/xentop/xentop.c b/tools/xenstat/xentop/xentop.c
index 2fd2b67..c465810 100644
--- a/tools/xenstat/xentop/xentop.c
+++ b/tools/xenstat/xentop/xentop.c
@@ -301,7 +301,7 @@ static void print(const char *fmt, ...)
 	if (!batch) {
 		if((current_row() < lines()-1)) {
 			va_start(args, fmt);
-			vwprintw(stdscr, (curses_str_t)fmt, args);
+			vw_printw(stdscr, (curses_str_t)fmt, args);
 			va_end(args);
 		}
 	} else {