btrfs: Remove logically dead code from btrfs_orphan_cleanup

In btrfs_orphan_cleanup the final 'if (ret) goto out' cannot ever be
executed. This is due to the last assignment to 'ret' depending on the
return value of btrfs_iget. If an error other than -ENOENT is returned
then the loop is prematurely terminated by 'goto out'.  On the other
hand, if the error value is ENOENT then a subsequent if branch is
executed that always re-assigns 'ret' and in case it's an error just
terminates the loop. No functional changes.

Coverity-id: 1437392
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>