reiserfs: change j_timestamp type to time64_t

reiserfs: change j_timestamp type to time64_t

[ Upstream commit 8b73ce6a4bae4fe12bcb2c361c0da4183c2e1b6f ]

This uses the deprecated time_t type but is write-only, and could be
removed, but as Jeff explains, having a timestamp can be usefule for
post-mortem analysis in crash dumps.

In order to remove one of the last instances of time_t, this changes the
type to time64_t, same as j_trans_start_time.

Link: http://lkml.kernel.org/r/20180622133315.221210-1-arnd@arndb.de
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jan Kara <jack@suse.cz>
Cc: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>