Suppress a warning

    com.c: In function 'grn_com_recv':
    com.c:861:3: warning: format '%lu' expects argument of type 'long unsigned int', but argument 7 has type 'uint32_t' [-Wformat=]
       GRN_LOG(ctx, GRN_LOG_INFO,
       ^

Is it OK to use "%u" for uint32_t?