Fix coverity issue in FindReflectometryLines

[rbauststfc]

We've had the following coverity issue reported for the FindReflectometryLines algorithm:

** CID 1563364: Performance inefficiencies (COPY_INSTEAD_OF_MOVE)
/jenkins_workdir/workspace/coverity_build_and_submit/Framework/Reflectometry/src/FindReflectometryLines2.cpp: 192 in Mantid::Reflectometry::FindReflectometryLines2::findPeak(const std::shared_ptrMantid::API::MatrixWorkspace &)()

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*** CID 1563364: Performance inefficiencies (COPY_INSTEAD_OF_MOVE)
/jenkins_workdir/workspace/coverity_build_and_submit/Framework/Reflectometry/src/FindReflectometryLines2.cpp: 192 in Mantid::Reflectometry::FindReflectometryLines2::findPeak(const std::shared_ptrMantid::API::MatrixWorkspace &)()
186 gaussian->setCentre(centreIndex);
187 gaussian->setFwhm(fwhm);
188 sum->addFunction(gaussian);
189 func = API::FunctionFactory::Instance().createFunction("LinearBackground");
190 func->setParameter("A0", medianY);
191 func->setParameter("A1", 0.);
CID 1563364: Performance inefficiencies (COPY_INSTEAD_OF_MOVE)
"func" is passed-by-value as parameter to "addFunction" when it could be moved instead.
192 sum->addFunction(func);
193 // call Fit child algorithm
194 auto fit = createChildAlgorithm("Fit");
195 fit->initialize();
196 fit->setProperty("Function", std::dynamic_pointer_castAPI::IFunction(sum));
197 fit->setProperty("InputWorkspace", transposedWS);