Dan Carpenter's static checker has found this error, it's introduced by
commit 64c043de
("Btrfs: fix up read_tree_block to return proper error")

It's really supposed to 'break' the loop on error like others.

Cc: Dan Carpenter <dan.carpenter@oracle.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>