curses: fix wchar_t printf warning

On some systems wchar_t is "long int", on others just "int".
So go cast to "long int" and adjust the printf format accordingly.

Reported-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20190402073018.17747-1-kraxel@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>