avcodec/ivi: Only clip samples when needed in ivi_output_plane()

435740 -> 396078 dezicycles
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ivi.c

@@ -913,6 +913,13 @@ static void ivi_output_plane(IVIPlaneDesc *plane, uint8_t *dst, ptrdiff_t dst_pi
         return;
 
     for (y = 0; y < plane->height; y++) {
+        int m = 0;
+        for (x = 0; x < plane->width; x++) {
+            int t = src[x] + 128;
+            dst[x] = t;
+            m |= t;
+        }
+        if (m & ~255)
             for (x = 0; x < plane->width; x++)
                 dst[x] = av_clip_uint8(src[x] + 128);
         src += pitch;