Fix missing offset in TBStore read from flash

This could cause incomplete data retrieval and mismatch when reading
data in more than one chunk, because every chunk would be read to the
same location at the beginning of the output buffer.

features/storage/kvstore/tdbstore/TDBStore.cpp

@@ -1418,7 +1418,7 @@ int TDBStore::do_reserved_data_get(void *reserved_data, size_t reserved_data_buf
 
     while (actual_size) {
         uint32_t chunk = std::min(work_buf_size, (uint32_t) actual_size);
-        ret = read_area(_active_area, offset, chunk, buf);
+        ret = read_area(_active_area, offset, chunk, buf + offset);
         if (ret) {
             return ret;
         }