check in opencl for MROUND to take exactly 2 arguments

Otherwise the mround unittest fails in opencl mode.

Change-Id: I6c8866495bbb44ff7dfc075ba4aac58d80dac7c7
Reviewed-on: https://gerrit.libreoffice.org/64240
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

sc/source/core/opencl/op_math.cxx

@@ -124,6 +124,7 @@ void OpSecH::GenSlidingWindowFunction(std::stringstream &ss,
 void OpMROUND::GenSlidingWindowFunction(std::stringstream &ss,
         const std::string &sSymName, SubArguments &vSubArguments)
 {
+    CHECK_PARAMETER_COUNT(2, 2);
     ss << "\ndouble " << sSymName;
     ss << "_"<< BinFuncName() <<"(";
     for (size_t i = 0; i < vSubArguments.size(); i++)