lavf/sr: fix the segmentation fault caused by incorrect input frame free.

This issue would cause segmetaion fault when running srcnn model with
sr filter by TensorFlow backend. This filter would free the frame incorectly.

Signed-off-by: Ting Fu <ting.fu@intel.com>

libavfilter/vf_sr.c

@@ -159,8 +159,9 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
         sws_scale(ctx->sws_uv_scale, (const uint8_t **)(in->data + 2), in->linesize + 2,
                   0, ctx->sws_uv_height, out->data + 2, out->linesize + 2);
     }
-
-    av_frame_free(&in);
+    if (in != out) {
+        av_frame_free(&in);
+    }
     return ff_filter_frame(outlink, out);
 }