corrected the function signature of the function that calculates heat capacity...

corrected the function signature of the function that calculates heat capacity of the liquid phase. 

This corrects a mistake originating from my last commit. 

reviewed by benjamin


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@9398 2fb0f335-1f38-0410-981e-8018bf24f1b0