avfilter/vsrc_mptestsrc: use hypot()

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>

libavfilter/vsrc_mptestsrc.c

@@ -240,7 +240,7 @@ static void ring2_test(uint8_t *dst, int dst_linesize, int off)
 
     for (y = 0; y < 16*16; y++) {
         for (x = 0; x < 16*16; x++) {
-            double d = sqrt((x-8*16)*(x-8*16) + (y-8*16)*(y-8*16));
+            double d = hypot(x-8*16, y-8*16);
             double r = d/20 - (int)(d/20);
             if (r < off/30.0) {
                 dst[x + y*dst_linesize]     = 255;