tests: fix audio recording test

To calculate frequency it needs to use samples per second (44100), not
samples pre recording lenght. This caused shorter recordings to not fit
into the margin.

qubes/tests/integ/vm_qrexec_gui.py

@@ -458,7 +458,7 @@ class TC_00_AppVMMixin(object):
                             (rec[:-1] < -threshold))[0]
         np.seterr('raise')
         # compare against sine wave frequency
-        rec_freq = rec_size/np.mean(np.diff(crossings))
+        rec_freq = 44100/np.mean(np.diff(crossings))
         if not sfreq*0.8 < rec_freq < sfreq*1.2:
             self.fail('frequency {} not in specified range'
                     .format(rec_freq))