fft-test: Use the float fabs() version

Fixes clang warning "absolute value function 'fabsf' given an argument
of type 'double' but has parameter of type 'float' which may cause
truncation of value [-Wabsolute-value]".

libavcodec/fft-test.c

@@ -193,7 +193,7 @@ static int check_diff(FFTSample *tab1, FFTSample *tab2, int n, double scale)
     double error = 0, max = 0;
 
     for (i = 0; i < n; i++) {
-        double e = fabsf(tab1[i] - (tab2[i] / scale)) / RANGE;
+        double e = fabs(tab1[i] - (tab2[i] / scale)) / RANGE;
         if (e >= 1e-3) {
             av_log(NULL, AV_LOG_ERROR, "ERROR %5d: "FMT" "FMT"\n",
                    i, tab1[i], tab2[i]);