ocfs2: o2hb: fix hb hung time

hr_last_timeout_start should be set as the last time where hb is
still OK.  When hb write timeout, hung time will be (jiffies -
hr_last_timeout_start).

Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Reviewed-by: Ryan Ding <ryan.ding@oracle.com>
Reviewed-by: Mark Fasheh <mfasheh@suse.de>
Cc: Gang He <ghe@suse.com>
Cc: rwxybh <rwxybh@126.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Joseph Qi <joseph.qi@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>