ocfs2: use time64_t to represent orphan scan times

struct timespec is not y2038 safe.  Use time64_t which is y2038 safe to
represent orphan scan times.  time64_t is sufficient here as only the
seconds delta times are relevant.

Also use appropriate time functions that return time in time64_t format.
Time functions now return monotonic time instead of real time as only
delta scan times are relevant and these values are not persistent across
reboots.

The format string for the debug print is still using long as this is
only the time elapsed since the last scan and long is sufficient to
represent this value.

Link: http://lkml.kernel.org/r/1475365138-20567-1-git-send-email-deepa.kernel@gmail.com
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Mark Fasheh <mfasheh@versity.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <jiangqi903@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>