jack_transport_reposition linkage fix

The second argument should be const, see 
https://github.com/jackaudio/jack2/blob/ec8403050c11cf6447a2a2f082f46fec8dc886cd/common/jack/transport.h#L191
and
https://github.com/jackaudio/jack2/blob/97e0e80bba707bc59ea1e6894590c1be6ae5a74d/common/JackAPI.cpp#L226