Btrfs: use right extent item position in send when finding extent clones

This was a leftover from the commit:

   74dd17fb
   (Btrfs: fix btrfs send for inline items and compression)
Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

fs/btrfs/send.c

@@ -1288,8 +1288,6 @@ static int find_extent_clone(struct send_ctx *sctx,
 		extent_item_pos = logical - found_key.objectid;
 	else
 		extent_item_pos = 0;
-
-	extent_item_pos = logical - found_key.objectid;
 	ret = iterate_extent_inodes(sctx->send_root->fs_info,
 					found_key.objectid, extent_item_pos, 1,
 					__iterate_backrefs, backref_ctx);