data parameter of dnxhd_encode_picture() should not be const.

Fixes "dnxhdenc.c:805: warning: initialization from incompatible pointer type".
patch by Daniel Verkamp, daniel drv nu

Originally committed as revision 18773 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/dnxhdenc.c

@@ -711,7 +711,7 @@ static void dnxhd_load_picture(DNXHDEncContext *ctx, const AVFrame *frame)
     ctx->cur_field = frame->interlaced_frame && !frame->top_field_first;
 }
 
-static int dnxhd_encode_picture(AVCodecContext *avctx, unsigned char *buf, int buf_size, const void *data)
+static int dnxhd_encode_picture(AVCodecContext *avctx, unsigned char *buf, int buf_size, void *data)
 {
     DNXHDEncContext *ctx = avctx->priv_data;
     int first_field = 1;