Fix rc4 header, #ifndef -> #define

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@10733 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavutil/rc4.h

@@ -19,7 +19,7 @@
  */
 
 #ifndef RC4_H
-#ifndef RC4_H
+#define RC4_H
 
 void ff_rc4_enc(const uint8_t *key, int keylen, uint8_t *data, int datalen);