Revert "matlab: fix quantization error calculation"

Just not sure what to do here, but the old way works much better. How to
fix, how to fix...

This reverts commit 441b9f67bfd46adc2bd845f2b4ac94a4cddb54cf.

Author: dhalperi

matlab/get_quant_err.m

@@ -23,9 +23,15 @@
     end
     thermal_noise_pwr = dbinv(noise_db);
 
-    % Take two: quantization error power can't ever be lower than ADC_BITS
-    % below RSSI
-    quant_error_pwr = dbinv(get_quant_err(csi_st, 6));
+    % Quantization error: the coefficients in the matrices are
+    % 8-bit signed numbers, max 127/-128 to min 0/1. Given that Intel
+    % only uses a 6-bit ADC, I expect every entry to be off by about
+    % +/- 1 (total across real & complex parts) per entry.
+    %
+    % The total power is then 1^2 = 1 per entry, and there are
+    % Nrx*Ntx entries per carrier. We only want one carrier's worth of
+    % error, since we only computed one carrier's worth of signal above.
+    quant_error_pwr = scale * (csi_st.Nrx * csi_st.Ntx);
 
     % Total noise and error power
     total_noise_pwr = thermal_noise_pwr + quant_error_pwr;