Fix webclient_write result issue.

webclient.c

@@ -978,7 +978,7 @@ struct webclient_session* webclient_open_custom(const char* URI, int method,
     if (data)
     {
         length = webclient_write(session, (unsigned char*) data, data_sz);
-        if (length != length)
+        if (length != data_sz)
         {
             rt_kprintf("POST data %d:%d\n", length, data_sz);
             goto _err_exit;
@@ -1029,7 +1029,7 @@ int webclient_transfer(const char* URI, const char* header, size_t header_sz,
 
     /* POST data */
     length = webclient_write(session, (unsigned char*) data, data_sz);
-    if (length != length)
+    if (length != data_sz)
     {
         rt_kprintf("POST data %d:%d\n", length, data_sz);
         goto __exit;