tmpfiles: fix device node major:minor logging to use i->major_minor

tmpfiles: fix device node major:minor logging to use i->major_minor

The debug log after creating a device node passed major(i->mode) and
minor(i->mode) to format the device number, but i->mode holds the
file permission bits (e.g. 0644), not the device number.

The device major:minor is stored in i->major_minor, which is also
what mknodat() receives. Use that field instead so the log correctly
reports the created device number.

Signed-off-by: dongshengyuan <dongshengyuan@uniontech.com>