drivers/rpmsgrtc: fix crash because list_node is not in server list

Fix potential crash when removing client from server list.
Add proper list initialization check before deletion operation.

Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>

drivers/timers/rpmsg_rtc.c

@@ -716,7 +716,11 @@ static void rpmsg_rtc_server_ept_release(FAR struct rpmsg_endpoint *ept)
   FAR struct rpmsg_rtc_server_s *server = ept->priv;
 
   nxmutex_lock(&server->lock);
-  list_delete(&client->node);
+  if (list_in_list(&client->node))
+    {
+      list_delete(&client->node);
+    }
+
   nxmutex_unlock(&server->lock);
   kmm_free(client);
 }