avcodec/mjpegdec: Use AVCodecInternal.in_pkt for buffer packet

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/mjpegdec.c

@@ -127,9 +127,7 @@ av_cold int ff_mjpeg_decode_init(AVCodecContext *avctx)
         s->picture_ptr = s->picture;
     }
 
-    s->pkt = av_packet_alloc();
-    if (!s->pkt)
-        return AVERROR(ENOMEM);
+    s->pkt = avctx->internal->in_pkt;
 
     s->avctx = avctx;
     ff_blockdsp_init(&s->bdsp, avctx);
@@ -2960,8 +2958,6 @@ av_cold int ff_mjpeg_decode_end(AVCodecContext *avctx)
     } else if (s->picture_ptr)
         av_frame_unref(s->picture_ptr);
 
-    av_packet_free(&s->pkt);
-
     av_frame_free(&s->smv_frame);
 
     av_freep(&s->buffer);