typerror in make_dics when using the csd as input

Describe the bug

typerror in make_dics when using the csd as input. The function make_dics give an error when the csd is given as input despite being computed with the mne csd_multitaper function

Steps to reproduce

csd_pooled=csd_multitaper(poolEpochs , fmin=21, fmax=22, bandwidth=10, n_jobs=1)
filters1 = make_dics(info=info, forward=fwd, csd=csd_pooled, reg=reg,reduce_rank=True,
                      pick_ori=None, real_filter=True,normalize_fwd=False,inversion='matrix', weight_norm=None) 

Expected results

filters weights

Actual results

File "/data/home1/epinzuti/anaconda3/lib/python3.7/site-packages/mne/beamformer/_dics.py", line 174, in make_dics
    info, fwd, csd = equalize_channels([info, forward, csd])

  File "<decorator-gen-31>", line 24, in equalize_channels

  File "/data/home1/epinzuti/anaconda3/lib/python3.7/site-packages/mne/channels/channels.py", line 148, in equalize_channels
    allowed_types_str)

  File "/data/home1/epinzuti/anaconda3/lib/python3.7/site-packages/mne/utils/check.py", line 389, in _validate_type
    % (item_name, type_name, type(item),))

TypeError: Instances to be modified must be an instance of Raw, Epochs, Evoked, TFR, Forward, Covariance, CrossSpectralDensity or Info, got <class 'mne.time_frequency.csd.CrossSpectralDensity'> instead

Start with the reproducer using csd_multitaper and make_dics, then inspect mne/beamformer/_dics.py where make_dics calls equalize_channels. Confirm why the CrossSpectralDensity instance is rejected and verify that the call completes and returns filter weights without the TypeError.