rtmp-services: Fix incompatible-pointer-types warnings

plugins/rtmp-services/rtmp-common.c

@@ -860,7 +860,7 @@ static const char **rtmp_common_get_supported_video_codecs(void *data)
 	struct rtmp_common *service = data;
 
 	if (service->video_codecs)
-		return service->video_codecs;
+		return (const char **)service->video_codecs;
 
 	struct dstr codecs = {0};
 	json_t *root = open_services_file();
@@ -895,7 +895,7 @@ static const char **rtmp_common_get_supported_video_codecs(void *data)
 
 fail:
 	json_decref(root);
-	return service->video_codecs;
+	return (const char **)service->video_codecs;
 }
 
 static const char *rtmp_common_username(void *data)