Add missing FFMPEG_ prefix to multiple inclusion guard.

Originally committed as revision 15047 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/avc.h

@@ -19,8 +19,8 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#ifndef AVC_H
-#define AVC_H
+#ifndef FFMPEG_AVC_H
+#define FFMPEG_AVC_H
 
 #include <stdint.h>
 #include "avio.h"
@@ -29,4 +29,4 @@ int ff_avc_parse_nal_units(const uint8_t *buf_in, uint8_t **buf, int *size);
 int ff_isom_write_avcc(ByteIOContext *pb, const uint8_t *data, int len);
 const uint8_t *ff_avc_find_startcode(const uint8_t *p, const uint8_t *end);
 
-#endif /* AVC_H */
+#endif /* FFMPEG_AVC_H */