Electrode height input doesn't work with DFN

[TomTranter]

Describe the bug
I think inputs need to be passed to discretisation in order to intialise the DFN model

To Reproduce

import pybamm
import numpy as np
pybamm.set_logging_level('INFO')

e_height = 0.25

model = pybamm.lithium_ion.DFN()
geometry = model.default_geometry
param = model.default_parameter_values
param.update(
    {
        "Electrode height [m]": "[input]",
    }
)
param.process_model(model)
param.process_geometry(geometry)
inputs= {
        "Electrode height [m]": e_height,
        }
A_cc = param.process_symbol(pybamm.geometric_parameters.A_cc).evaluate(u=inputs)
var = pybamm.standard_spatial_vars
var_pts = {var.x_n: 5, var.x_s: 5, var.x_p: 5, var.r_n: 10, var.r_p: 10}
spatial_methods = model.default_spatial_methods

solver = model.default_solver
sim = pybamm.Simulation(
    model=model,
    geometry=geometry,
    parameter_values=param,
    var_pts=var_pts,
    spatial_methods=spatial_methods,
    solver=solver,
)
sim.solve(t_eval=np.linspace(0, 0.05, 100), inputs=inputs)

[valentinsulzer]

Have pushed a hacky workaround for now. It only works with the scikits dae or casadi solver.