Update GMDS and GMGP definitions in GenericOutputBlackoilModule.cpp

Should GMDS be CO2 dissolved in water phase and GMGP be CO2 in gas phase (rather than the other way around)?

opm/simulators/flow/GenericOutputBlackoilModule.cpp

@@ -122,10 +122,10 @@ std::string EclString(const Opm::Inplace::Phase phase)
         return "GMIP";
 
     case Opm::Inplace::Phase::CO2MassInWaterPhase:
-        return "GMGP";
+        return "GMDS";
 
     case Opm::Inplace::Phase::CO2MassInGasPhase:
-        return "GMDS";
+        return "GMGP";
 
     case Opm::Inplace::Phase::CO2MassInGasPhaseInMob:
         return "GMTR";