update Steves heuristic noise index calculation

fsl_regfilt.cc

@@ -260,8 +260,8 @@ int calc_freqindex(){
 			tempVol.threshold(0.0);
 			for(int ctr = 0; ctr < design.Ncols(); ctr++ )
 				scores(1,ctr+1) = tempVol[ctr].percentile(0.99,mask);
-			scores-=scores.MinimumAbsoluteValue();
 			scores/=scores.MaximumAbsoluteValue();
+			scores-=scores.MinimumAbsoluteValue();
 			if(debug.value()) cerr << " initial scores: " << scores << endl;
 		}
 		scores = SP(scores,sum_ratio);