Added a missing const to ff_h264_get_slice_type().

Originally committed as revision 21421 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264.c

@@ -2147,7 +2147,7 @@ static int decode_slice_header(H264Context *h, H264Context *h0){
     return 0;
 }
 
-int ff_h264_get_slice_type(H264Context *h)
+int ff_h264_get_slice_type(const H264Context *h)
 {
     switch (h->slice_type) {
     case FF_P_TYPE:  return 0;

libavcodec/h264.h

@@ -617,7 +617,7 @@ av_cold void ff_h264_free_context(H264Context *h);
 /**
  * reconstructs bitstream slice_type.
  */
-int ff_h264_get_slice_type(H264Context *h);
+int ff_h264_get_slice_type(const H264Context *h);
 
 /**
  * allocates tables.