Fixes compilation of WellContributions with deactivated OpenCL.

OpenCL header was included and OpenclKernels used unconditionally
in WellContributions.cpp. As this file is compiled if CUDA is found,
too it lead to undefined references for e.g. cl::CommandQueue if
opencl headers were there and compile error if not.

opm/simulators/linalg/bda/WellContributions.cpp

@@ -23,13 +23,14 @@
 #include <opm/common/OpmLog/OpmLog.hpp>
 #include <opm/common/ErrorMacros.hpp>
 
-#include <opm/simulators/linalg/bda/openclKernels.hpp>
 #include <opm/simulators/linalg/bda/WellContributions.hpp>
 
 namespace Opm
 {
 
+#if HAVE_OPENCL
 using Opm::Accelerator::OpenclKernels;
+#endif
 
 WellContributions::WellContributions(std::string accelerator_mode, bool useWellConn){
     if(accelerator_mode.compare("cusparse") == 0){