avidec: add missing initializer braces to shut up gcc warning.

This fixes the warning:
    libavformat/avidec.c:81:5: warning: missing braces around initializer [-Wmissing-braces]

libavformat/avidec.c

@@ -78,7 +78,7 @@ typedef struct {
 
 
 static const AVOption options[] = {
-    { "use_odml", "use odml index", offsetof(AVIContext, use_odml), FF_OPT_TYPE_INT, 1, -1, 1, AV_OPT_FLAG_DECODING_PARAM},
+    { "use_odml", "use odml index", offsetof(AVIContext, use_odml), FF_OPT_TYPE_INT, {.dbl = 1}, -1, 1, AV_OPT_FLAG_DECODING_PARAM},
     { NULL },
 };