this is necessary to allow non-trivial ParameterCache objects with
Local-AD evaluations. So far, the only fluid system in opm-material
which needs this is the Spe5 fluid system (which is unused by eWoms),
but sooner or later this change would have been required anyway.
Note that it is possible that this patch is errornous if Evaluation !=
Scalar for a fluid system that uses a non-trivial ParameterCache
object, but the errors should be relatively easy to fix...