reiserfs: use monotonic time for j_trans_start_time

reiserfs: use monotonic time for j_trans_start_time

Using CLOCK_REALTIME time_t timestamps breaks on 32-bit systems in 2038,
and gives surprising results with a concurrent settimeofday().

This changes the reiserfs journal timestamps to use ktime_get_seconds()
instead, which makes it use a 64-bit CLOCK_MONOTONIC stamp.

In the procfs output, the monotonic timestamp needs to be converted back
to CLOCK_REALTIME to keep the existing ABI.

Link: http://lkml.kernel.org/r/20180620142522.27639-2-arnd@arndb.de
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>