Make register_protocol() use the function av_register_protocol2()

rather than av_register_protocol(), which is deprecated.
Fix the GCC warning:
avio.c: In function ‘register_protocol’:
avio.c:93: warning: ‘av_register_protocol’ is deprecated (declared at avio.c:86)

Originally committed as revision 25267 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/avio.c

@@ -90,7 +90,7 @@ int av_register_protocol(URLProtocol *protocol)
 
 int register_protocol(URLProtocol *protocol)
 {
-    return av_register_protocol(protocol);
+    return av_register_protocol2(protocol, sizeof(struct URLProtocol_compat));
 }
 #endif