stats: Functions with no arguments should specify(void)

... otherwise callers might pass arbitrary arguments without raising
a compiler error or warning.

Change-Id: Ia2de1d13df5f00dcc42493090734a635029d76b5
diff --git a/include/osmocom/core/stats.h b/include/osmocom/core/stats.h
index 6544dfa..a034a61 100644
--- a/include/osmocom/core/stats.h
+++ b/include/osmocom/core/stats.h
@@ -108,7 +108,7 @@
 extern struct osmo_stats_config *osmo_stats_config;
 
 void osmo_stats_init(void *ctx);
-int osmo_stats_report();
+int osmo_stats_report(void);
 
 int osmo_stats_set_interval(int interval);