lavc/mpegvideo: add missing const

Signed-off-by: Lukasz Marek <lukasz.m.luki@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mpegvideo.h

@@ -800,7 +800,7 @@ void ff_MPV_frame_end(MpegEncContext *s);
 int ff_MPV_encode_init(AVCodecContext *avctx);
 int ff_MPV_encode_end(AVCodecContext *avctx);
 int ff_MPV_encode_picture(AVCodecContext *avctx, AVPacket *pkt,
-                          AVFrame *frame, int *got_packet);
+                          const AVFrame *frame, int *got_packet);
 void ff_dct_encode_init_x86(MpegEncContext *s);
 void ff_MPV_common_init_x86(MpegEncContext *s);
 void ff_MPV_common_init_axp(MpegEncContext *s);

libavcodec/mpegvideo_enc.c

@@ -1603,7 +1603,7 @@ static int frame_start(MpegEncContext *s)
 }
 
 int ff_MPV_encode_picture(AVCodecContext *avctx, AVPacket *pkt,
-                          AVFrame *pic_arg, int *got_packet)
+                          const AVFrame *pic_arg, int *got_packet)
 {
     MpegEncContext *s = avctx->priv_data;
     int i, stuffing_count, ret;