avfilter/vf_scale: store the offset in a local variable before adding it

Signed-off-by: James Almer <jamrial@gmail.com>

libavfilter/vf_scale.c

@@ -632,10 +632,12 @@ static int scale_slice(AVFilterLink *link, AVFrame *out_buf, AVFrame *cur_pic, s
 
     for (i=0; i<4; i++) {
         int vsub= ((i+1)&2) ? scale->vsub : 0;
+        ptrdiff_t  in_offset = ((y>>vsub)+field) * cur_pic->linesize[i];
+        ptrdiff_t out_offset =            field  * out_buf->linesize[i];
          in_stride[i] = cur_pic->linesize[i] * mul;
         out_stride[i] = out_buf->linesize[i] * mul;
-         in[i] = FF_PTR_ADD(cur_pic->data[i], ((y>>vsub)+field) * cur_pic->linesize[i]);
-        out[i] = FF_PTR_ADD(out_buf->data[i],            field  * out_buf->linesize[i]);
+         in[i] = FF_PTR_ADD(cur_pic->data[i],  in_offset);
+        out[i] = FF_PTR_ADD(out_buf->data[i], out_offset);
     }
     if (scale->input_is_pal)
          in[1] = cur_pic->data[1];