btrfs: fold btrfs_clone_ordered_extent into btrfs_split_ordered_extent
The function btrfs_clone_ordered_extent is very specific to the usage in
btrfs_split_ordered_extent. Now that only a single call to
btrfs_clone_ordered_extent is left, just fold it into
btrfs_split_ordered_extent to make the operation more clear.
Reviewed-by: Josef Bacik <josef@toxicpanda.com> Tested-by: Johannes Thumshirn <johannes.thumshirn@wdc.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: David Sterba <dsterba@suse.com>