staging/lustre: use 64-bit time for debugfs output

This time is only printed in debugfs, and can be easily converted
to 64-bit to avoid overflowing on 32-bit systems in 2038.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>