mpegvideo: fix constness error in ff_MPV_encode_picture()

The struct has some of its fields changed, thus is not strictly const.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mpegvideo.h

@@ -750,7 +750,7 @@ 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,
-                          const AVFrame *frame, int *got_packet);
+                          AVFrame *frame, int *got_packet);
 void ff_MPV_common_init_mmx(MpegEncContext *s);
 void ff_MPV_common_init_axp(MpegEncContext *s);
 void ff_MPV_common_init_mmi(MpegEncContext *s);

libavcodec/mpegvideo_enc.c

@@ -1418,7 +1418,7 @@ no_output_pic:
 }
 
 int ff_MPV_encode_picture(AVCodecContext *avctx, AVPacket *pkt,
-                          const AVFrame *pic_arg, int *got_packet)
+                          AVFrame *pic_arg, int *got_packet)
 {
     MpegEncContext *s = avctx->priv_data;
     int i, stuffing_count, ret;