Tools: Tune: dcblock: Avoid warning about ignoring imaginary

The abs() function need to be added to plot the correct magnitude
response. Matlab warned in this case about ignoring imaginary
part.

Signed-off-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>

Author: singalsu

tools/tune/dcblock/dcblock_plot_transferfn.m

@@ -7,7 +7,7 @@
 
 f = linspace(1, fs/2, 500);
 
-semilogx(f, 20*log10(freqz(b, a, f, fs)));
+semilogx(f, 20*log10(abs(freqz(b, a, f, fs))));
 grid on
 xlabel('Frequency (Hz)');
 ylabel('Magnitude (dB)');