Fix clang compiler warnings.

.../GridGenerator/utilities/transformator/TransformatorImp.h

...aStructureInitializer/GridReaderGenerator/GridGenerator.h

src/gpu/VirtualFluids_GPU/FindInterface/FindInterface.cpp

src/gpu/VirtualFluids_GPU/Input/PositionReader.cpp

src/gpu/VirtualFluids_GPU/Kernel/Kernel.h

...Utilities/CheckParameterStrategy/CheckParameterStrategy.h

...Fluids_GPU/Kernel/Utilities/KernelFactory/KernelFactory.h

...s_GPU/Kernel/Utilities/Mapper/KernelMapper/KernelMapper.h

src/gpu/VirtualFluids_GPU/Parameter/Parameter.cpp

src/gpu/VirtualFluids_GPU/PreProcessor/PreProcessor.h

...PU/PreProcessor/PreProcessorFactory/PreProcessorFactory.h