logd: compile warning message

Change-Id: I7ddd010031299395cad96f1743d7a7e6a6866b4c
diff --git a/logd/LogListener.cpp b/logd/LogListener.cpp
index bef2097..104a2eb 100644
--- a/logd/LogListener.cpp
+++ b/logd/LogListener.cpp
@@ -50,7 +50,7 @@
     int socket = cli->getSocket();
 
     ssize_t n = recvmsg(socket, &hdr, 0);
-    if (n <= (sizeof_log_id_t + sizeof(uint16_t) + sizeof(log_time))) {
+    if (n <= (ssize_t)(sizeof_log_id_t + sizeof(uint16_t) + sizeof(log_time))) {
         return false;
     }