staging/lustre: use 64-bit timestamps in debugfs output

Some lustre debugfs files contain the current time. Make sure
we use a format here that does not overflow 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>