Add back in the mpi libs to OSPRAY_LIBRARIES if MPI was enabled
Add back in the mpi libs to OSPRAY_LIBRARIES if MPI was enabled

This got removed or lost for some reason in some commit?

ospray/OSPRay,MengjiaoH/ospray,MengjiaoH/ospray,wilsonCernWq/ospray,MengjiaoH/ospray,ospray/OSPRay,MengjiaoH/ospray,ospray/OSPRay,wilsonCernWq/ospray,ospray/OSPRay,wilsonCernWq/ospray,MengjiaoH/ospray