Fixes typo in CMake option HYTEG_BUILD_WITH_OPENMP
[91cbadeb] changed the option name from WALBERLA_BUILD_WITH_OPENMP to HYETG_BUILD_WITH_OPENMP with a letter transposition.
[91cbadeb] changed the option name from WALBERLA_BUILD_WITH_OPENMP to HYETG_BUILD_WITH_OPENMP with a letter transposition.