Fix matfaust.dst complex(sparse_matrix) error for older versions of Matlab.

Matlab R2022b doesn't need this fix.

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Error occurred in FaustFactoryTest/test_dst and it did not run to
completion.

    ---------
    Error ID:
    ---------
    'MATLAB:complex:expectsFullNumeric'

    --------------
    Error Details:
    --------------
    Error using complex
    Input A must be numeric and full.

    Error in matfaust.dst>mod_fft (line 160)
        F = matfaust.Faust([Bs, {complex(bitrev_perm(N))}],
varargin{:});

    Error in matfaust.dst (line 90)
        MDFT = mod_fft(n, 'dev', dev);

    Error in FaustFactoryTest/test_dst (line 846)
                DST = matfaust.dst(n, 'normed', false);
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