btrfs: drop unused parameter path from btrfs_tree_mod_log_rewind()

The path parameter was used for our own locking, that got converted to
rwsem eventually. Last usage in ac5887c8 ("btrfs: locking: remove
all the blocking helpers").

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>