vaapi: Disable deprecation warnings around use of old struct vaapi_context

libavcodec/vaapi_decode.h

@@ -59,9 +59,11 @@ typedef struct VAAPIDecodeContext {
     VAContextID           va_context;
 
 #if FF_API_STRUCT_VAAPI_CONTEXT
+FF_DISABLE_DEPRECATION_WARNINGS
     int                   have_old_context;
     struct vaapi_context *old_context;
     AVBufferRef          *device_ref;
+FF_ENABLE_DEPRECATION_WARNINGS
 #endif
 
     AVHWDeviceContext    *device;