avutil/version: add FF_CONST_AVUTIL53

This will become "const" on the next major API version
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/version.h

@@ -138,6 +138,14 @@
 #define FF_API_OPT_TYPE_METADATA        (LIBAVUTIL_VERSION_MAJOR < 54)
 #endif
 
+#ifndef FF_CONST_AVUTIL53
+#if LIBAVUTIL_VERSION_MAJOR >= 53
+#define FF_CONST_AVUTIL53 const
+#else
+#define FF_CONST_AVUTIL53
+#endif
+#endif
+
 /**
  * @}
  */