statsd: Fix compiler warning (int32_t vs. int64_t)

Fixes the following compiler warning:

stats_statsd.c: In function ‘osmo_stats_reporter_create_statsd’: stats_statsd.c:54:18: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
  srep->send_item = osmo_stats_reporter_statsd_send_item;

Change-Id: Id36914906e0982f6ac092a311210727de66b343a
diff --git a/src/stats.c b/src/stats.c
index 5f1d028..1efc8cd 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -62,7 +62,7 @@
 	int64_t value, int64_t delta);
 static int osmo_stats_reporter_log_send_item(struct osmo_stats_reporter *srep,
 	const struct osmo_stat_item_group *statg,
-	const struct osmo_stat_item_desc *desc, int value);
+	const struct osmo_stat_item_desc *desc, int64_t value);
 
 static int update_srep_config(struct osmo_stats_reporter *srep)
 {
@@ -429,7 +429,7 @@
 
 static int osmo_stats_reporter_log_send_item(struct osmo_stats_reporter *srep,
 	const struct osmo_stat_item_group *statg,
-	const struct osmo_stat_item_desc *desc, int value)
+	const struct osmo_stat_item_desc *desc, int64_t value)
 {
 	return osmo_stats_reporter_log_send(srep, "i",
 		statg->desc->group_name_prefix, statg->idx,