argument fix in initGrids call

somehow the order of localGrid and globalGrid arguments was changed
in Environment.initGrid vs. Subgrid.init, meaning initGrid crossforwards
it's arguments to init, which I find not beautiful and resulted in an
assert error:
   picongpu/src/libPMacc/include/mappings/simulation/SubGrid.hpp:50:
    PMacc::SimulationBox<DIM>::SimulationBox(const Size&, const Size&,
    const Size&) [with unsigned int DIM = 2u, PMacc::SimulationBox<DIM>
    ::Size = PMacc::DataSpace<2u>]: Assertion `localSize[i] <=
    globalSize[i]' failed.