lavc/qsvdec: return 0 if more data is required

The type of qsv decoders is FF_CODEC_CB_TYPE_DECODE which must not
return AVERROR(EAGAIN). commit 42b20c9 added an assertion to check the
returned value.

Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>
(cherry picked from commit e233f3e75f)

libavcodec/qsvdec.c

@@ -1076,6 +1076,9 @@ static int qsv_decode_frame(AVCodecContext *avctx, AVFrame *frame,
 
         ret = qsv_process_data(avctx, &s->qsv, frame, got_frame, &s->buffer_pkt);
         if (ret < 0){
+            if (ret == AVERROR(EAGAIN))
+                ret = 0;
+
             /* Drop buffer_pkt when failed to decode the packet. Otherwise,
                the decoder will keep decoding the failure packet. */
             av_packet_unref(&s->buffer_pkt);