multimedia/plexhometheater: unbreak build after r425442

xbmc/cores/dvdplayer/DVDPlayerAudioResampler.cpp:77:12: error:

    cannot initialize a variable of type 'float *' with an lvalue of type 'const float *'
float*   outputptr = m_converterdata.data_in;
         ^           ~~~~~~~~~~~~~~~~~~~~~~~

Reported by: pkg-fallout
Pointy hat to: @bapt (and upstream)
Approved by: portmgr blanket