bench: fix incomplete refactoring

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Author: kgryte

lib/node_modules/@stdlib/complex/float64/base/mul-add/benchmark/c/benchmark.c

@@ -115,8 +115,8 @@ static double benchmark( void ) {
 
 	t = tic();
 	for ( i = 0; i < ITERATIONS; i++ ) {
-		re = ( creal(z1)*creal(z2) ) - ( cimag(z1)*cimag(z2) ) + creal(z3);
-		im = ( creal(z1)*cimag(z2) ) + ( cimag(z1)*creal(z2) ) + cimag(z3);
+		re = ( creal(z1[i%100])*creal(z2[i%100]) ) - ( cimag(z1[i%100])*cimag(z2[i%100]) ) + creal(z3[i%100]);
+		im = ( creal(z1[i%100])*cimag(z2[i%100]) ) + ( cimag(z1[i%100])*creal(z2[i%100]) ) + cimag(z3[i%100]);
 		z4 = re + im*I;
 		if ( z4 != z4 ) {
 			printf( "should not return NaN\n" );