avfilter/vf_ssim: fix some cosmetics issues

Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavfilter/vf_ssim.c

@@ -139,7 +139,7 @@ static float ssim_end4(int sum0[5][4], int sum1[5][4], int width)
     float ssim = 0.0;
     int i;
 
-    for( i = 0; i < width; i++ )
+    for (i = 0; i < width; i++)
         ssim += ssim_end1(sum0[i][0] + sum0[i + 1][0] + sum1[i][0] + sum1[i + 1][0],
                           sum0[i][1] + sum0[i + 1][1] + sum1[i][1] + sum1[i + 1][1],
                           sum0[i][2] + sum0[i + 1][2] + sum1[i][2] + sum1[i + 1][2],