nilfs2: Switch to use %ptTs

Use %ptTs instead of open coded variant to print contents
of time64_t type in human readable form.

Use sysfs_emit() at the same time in the changed functions.

Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: linux-nilfs@vger.kernel.org
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210511153958.34527-3-andriy.shevchenko@linux.intel.com