avcodec/xiph: make extradata argument const

Fixes "warning: passing argument 1 of avpriv_split_xiph_headers discards const qualifier from pointer target type"
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/xiph.c

@@ -21,7 +21,7 @@
 #include "libavutil/intreadwrite.h"
 #include "xiph.h"
 
-int avpriv_split_xiph_headers(uint8_t *extradata, int extradata_size,
+int avpriv_split_xiph_headers(const uint8_t *extradata, int extradata_size,
                           int first_header_size, uint8_t *header_start[3],
                           int header_len[3])
 {

libavcodec/xiph.h

@@ -36,7 +36,7 @@
  * @param[out] header_len The sizes of each of the three headers.
  * @return On error a negative value is returned, on success zero.
  */
-int avpriv_split_xiph_headers(uint8_t *extradata, int extradata_size,
+int avpriv_split_xiph_headers(const uint8_t *extradata, int extradata_size,
                               int first_header_size, uint8_t *header_start[3],
                               int header_len[3]);