lavf/rtpproto: Use the correct patch when including poll.h

Fixes a warning using musl:
In file included from libavformat/rtpproto.c:43:0:
/usr/local/musl/include/sys/poll.h:1:2: warning: #warning redirecting incorrect #include <sys/poll.h> to <poll.h>

libavformat/rtpproto.c

@@ -40,7 +40,7 @@
 #include "os_support.h"
 #include <fcntl.h>
 #if HAVE_POLL_H
-#include <sys/poll.h>
+#include <poll.h>
 #endif
 
 typedef struct RTPContext {