btrfs: free list element sooner at log_new_dir_dentries()

At log_new_dir_dentries(), there's no need to keep the current list
element allocated while processing the leaves with directory items for
the current directory, and while logging other inodes. Plus in case we
find a subdirectory, we also end up allocating a new list element while
the current one is still allocated, temporarily using more memory than
necessary.

So free the current list element early on, before processing leaves.
Also make the removal and release of all list elements in case of an
error more simple by eliminating the label and goto, adding an explicit
loop to release all list elements in case an error happens.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>