chan_dahdi: Fix analog parking using flash-hook.

Transferring an analog call using a flash-hook to parking would fail to
park the call and result in an invalid ao2 object unref.

* Park the correct bridged channel.
........

Merged revisions 400236 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@400237 65c4cc65-6c06-0410-ace0-fbb531ad65f3