btrfs: remove pointless data_end assignment in btrfs_extent_item()

There's no point in setting 'data_end' to 'old_data' as we don't use it
afterwards. So remove the redundant assignment which was never needed
and added when the function was first added in commit 6567e83
("Btrfs: early work to file_write in big extents").

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

Author: fdmanana

fs/btrfs/ctree.c

@@ -4136,7 +4136,6 @@ void btrfs_extend_item(struct btrfs_trans_handle *trans,
 	memmove_leaf_data(leaf, data_end - data_size, data_end,
 			  old_data - data_end);
 
-	data_end = old_data;
 	old_size = btrfs_item_size(leaf, slot);
 	btrfs_set_item_size(leaf, slot, old_size + data_size);
 	btrfs_mark_buffer_dirty(trans, leaf);