avcodec/decode: Update decode_simple_internal() to get the side data correctly.

Use avci->last_pkt_props to get the side data. Using |pkt| doesn't work
when FF_API_MERGE_SD is set, as the compressed side data is expanded into
|tmp|, leaving the original |pkt| unchanged.

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

libavcodec/decode.c

@@ -462,7 +462,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
                 frame->sample_rate = avctx->sample_rate;
         }
 
-        side= av_packet_get_side_data(pkt, AV_PKT_DATA_SKIP_SAMPLES, &side_size);
+        side= av_packet_get_side_data(avci->last_pkt_props, AV_PKT_DATA_SKIP_SAMPLES, &side_size);
         if(side && side_size>=10) {
             avctx->internal->skip_samples = AV_RL32(side) * avctx->internal->skip_samples_multiplier;
             discard_padding = AV_RL32(side + 4);