staging/lustre: use 64-bit ibn_incarnation computation

ibn_incarnation is a 64-bit value, but using timeval to compute
it will cause an overflow in 2038. This changes it to use
ktime_get_real_ts64() instead.

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>