fs/reiserfs/journal.c: delete useless variables

The value of 'cn' is not used, so just delete it.

Link: https://lore.kernel.org/r/1618278196-17749-1-git-send-email-tiantao6@hisilicon.com


Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Jan Kara <jack@suse.cz>