Correct missing return value.

server/modules/routing/binlog/blr_slave.c

@@ -1614,7 +1614,7 @@ ROUTER_INSTANCE		*router = slave->router;
          * because the "data" parameter will not contain meaningful data,
          * so we have no choice but to stop here.
          */
-        return;
+        return 0;
     }
 	if (reason == DCB_REASON_DRAINED)
 	{

server/modules/routing/readconnroute.c

@@ -1017,7 +1017,7 @@ static int handle_state_switch(DCB* dcb,DCB_REASON reason, void * routersession)
          * We cannot handle a DCB that does not have a router session,
          * except in the case where error processing is invoked.
          */
-        return;
+        return 0;
     }
     switch(reason)
     {

server/modules/routing/readwritesplit/readwritesplit.c

@@ -5309,7 +5309,7 @@ static int router_handle_state_switch(
          * because the "data" parameter will not contain meaningful data,
          * so we have no choice but to stop here.
          */
-        return;
+        return 0;
     }
         bref = (backend_ref_t *)data;
         CHK_BACKEND_REF(bref);

server/modules/routing/schemarouter/schemarouter.c

@@ -4412,7 +4412,7 @@ router_handle_state_switch(
          * because the "data" parameter will not contain meaningful data,
          * so we have no choice but to stop here.
          */
-        return;
+        return 0;
     }
     bref = (backend_ref_t *) data;
     CHK_BACKEND_REF(bref);