mark qtrle input data as const.

Originally committed as revision 11820 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/qtrle.c

@@ -45,7 +45,7 @@ typedef struct QtrleContext {
     DSPContext dsp;
     AVFrame frame;
 
-    unsigned char *buf;
+    const unsigned char *buf;
     int size;
 
 } QtrleContext;
@@ -530,7 +530,7 @@ static int qtrle_decode_init(AVCodecContext *avctx)
 
 static int qtrle_decode_frame(AVCodecContext *avctx,
                               void *data, int *data_size,
-                              uint8_t *buf, int buf_size)
+                              const uint8_t *buf, int buf_size)
 {
     QtrleContext *s = avctx->priv_data;