fix build litiv/3rdparty/ofdis/include/litiv/3rdparty/ofdis/ofdis.hpp…

[michelpromonet]

Hi,

This pull request is fixing compilation that fails with error:

Scanning dependencies of target litiv_3rdparty_ofdis
[  7%] Building CXX object 3rdparty/ofdis/CMakeFiles/litiv_3rdparty_ofdis.dir/src/ofdis.cpp.o
In file included from litiv/3rdparty/ofdis/src/ofdis.cpp:5:
litiv/3rdparty/ofdis/include/litiv/3rdparty/ofdis/ofdis.hpp:24:21: error: friend declaration of ‘void computeFlow(const cv::Mat&, const cv::Mat&, cv::Mat&, ofdis::FlowParams)’ specifies default arguments and isn’t a definition [-fpermissive]
   24 |         friend void computeFlow(const cv::Mat&,const cv::Mat&,cv::Mat&,FlowParams=FlowParams());
      |                     ^~~~~~~~~~~
compilation terminated due to -Wfatal-errors.

[plstcharles]

LGTM, thanks for the fix!