avfilter/framesync: fix order of operation with = and <0

Reviewed-by: Sean McGovern <gseanmcg@gmail.com>
Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 9450a4a7fe)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/framesync.c

@@ -288,7 +288,7 @@ int ff_framesync_get_frame(FFFrameSync *fs, unsigned in, AVFrame **rframe,
         if (need_copy) {
             if (!(frame = av_frame_clone(frame)))
                 return AVERROR(ENOMEM);
-            if ((ret = ff_inlink_make_frame_writable(fs->parent->inputs[in], &frame) < 0)) {
+            if ((ret = ff_inlink_make_frame_writable(fs->parent->inputs[in], &frame)) < 0) {
                 av_frame_free(&frame);
                 return ret;
             }