[doxygen] fix doxygen in fluidmatrixinteractions

.../fluidmatrixinteractions/1p/thermalconductivityaverage.hh

dumux/material/fluidmatrixinteractions/2p/brookscorey.hh

.../material/fluidmatrixinteractions/2p/brookscoreyparams.hh

dumux/material/fluidmatrixinteractions/2p/efftoabslaw.hh

.../material/fluidmatrixinteractions/2p/efftoabslawparams.hh

dumux/material/fluidmatrixinteractions/2p/heatpipelaw.hh

.../material/fluidmatrixinteractions/2p/heatpipelawparams.hh

dumux/material/fluidmatrixinteractions/2p/linearmaterial.hh

...terial/fluidmatrixinteractions/2p/linearmaterialparams.hh

dumux/material/fluidmatrixinteractions/2p/philtophoblaw.hh

...rial/fluidmatrixinteractions/2p/regularizedbrookscorey.hh

...luidmatrixinteractions/2p/regularizedbrookscoreyparams.hh

...l/fluidmatrixinteractions/2p/regularizedlinearmaterial.hh

...dmatrixinteractions/2p/regularizedlinearmaterialparams.hh

...ial/fluidmatrixinteractions/2p/regularizedvangenuchten.hh

...uidmatrixinteractions/2p/regularizedvangenuchtenparams.hh

...fluidmatrixinteractions/2p/thermalconductivityjohansen.hh

...xinteractions/2p/thermalconductivitysimplefluidlumping.hh

...fluidmatrixinteractions/2p/thermalconductivitysomerton.hh

dumux/material/fluidmatrixinteractions/2p/vangenuchten.hh