Typeo in my previous commit: was sending the wrong buffer to the server!

Was sending the incorrect buffer to the server for the last step in the SASL QOP negotiation process.

This bug was causing the client to send back the buffer the server was sending instead of selecting a QOP from the list the server provided and sending it back.  This would cause the server to use a different QOP than the client was expecting in some circumstances.  It is a one line fix :-)