avcodec/mpegvideodec: Constify some functions

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

libavcodec/mpegvideo_dec.c

@@ -497,14 +497,14 @@ void ff_mpv_frame_end(MpegEncContext *s)
         ff_thread_report_progress(&s->current_picture_ptr->tf, INT_MAX, 0);
 }
 
-void ff_print_debug_info(MpegEncContext *s, Picture *p, AVFrame *pict)
+void ff_print_debug_info(const MpegEncContext *s, const Picture *p, AVFrame *pict)
 {
     ff_print_debug_info2(s->avctx, pict, s->mbskip_table, p->mb_type,
                          p->qscale_table, p->motion_val,
                          s->mb_width, s->mb_height, s->mb_stride, s->quarter_sample);
 }
 
-int ff_mpv_export_qp_table(MpegEncContext *s, AVFrame *f, Picture *p, int qp_type)
+int ff_mpv_export_qp_table(const MpegEncContext *s, AVFrame *f, const Picture *p, int qp_type)
 {
     AVVideoEncParams *par;
     int mult = (qp_type == FF_MPV_QSCALE_TYPE_MPEG1) ? 2 : 1;

libavcodec/mpegvideodec.h

@@ -53,12 +53,12 @@ int ff_mpv_frame_start(MpegEncContext *s, AVCodecContext *avctx);
 void ff_mpv_report_decode_progress(MpegEncContext *s);
 void ff_mpv_frame_end(MpegEncContext *s);
 
-int ff_mpv_export_qp_table(MpegEncContext *s, AVFrame *f, Picture *p, int qp_type);
+int ff_mpv_export_qp_table(const MpegEncContext *s, AVFrame *f, const Picture *p, int qp_type);
 int ff_mpeg_update_thread_context(AVCodecContext *dst, const AVCodecContext *src);
 void ff_mpeg_draw_horiz_band(MpegEncContext *s, int y, int h);
 void ff_mpeg_flush(AVCodecContext *avctx);
 
-void ff_print_debug_info(MpegEncContext *s, Picture *p, AVFrame *pict);
+void ff_print_debug_info(const MpegEncContext *s, const Picture *p, AVFrame *pict);
 
 static inline int mpeg_get_qscale(MpegEncContext *s)
 {