solo.qli: Make consistent with updated irf_spectrogram()

Change to make consistent with updated irf_spectrogram() behaviour.

irf_spectrogram()'s behaviour when being instructed to *do a log plot*
(w.r.t. to color/intensity) was updated
(a) from doing linear plot if data contained negative values,
(b) to always doing log plot

Changed call (ellipticity):
irf_spectrogram(h(4), Specrec, 'log', 'donotfitcolorbarlabel');
log --> lin

modified:   generate_quicklooks_24h_6h_2h.m

mission/solar_orbiter/+solo/+qli/generate_quicklooks_24h_6h_2h.m

@@ -281,7 +281,7 @@ function generate_quicklooks_24h_6h_2h(Data, OutputPaths, Tint24h, logoPath)
     Specrec.p       = ellipticity;
     Specrec.f_label = '';
     Specrec.p_label = {'Ellipticity', 'DOP>0.7'};
-    irf_spectrogram(h(4), Specrec, 'log', 'donotfitcolorbarlabel');
+    irf_spectrogram(h(4), Specrec, 'lin', 'donotfitcolorbarlabel');
     set(     h(4), 'yscale', 'log');
     % set(h(1), 'ytick', [1e1 1e2 1e3]);
     caxis(   h(4), [-1 1])