ucc/hdlc: fix two little issue

1. modify bd_status from u32 to u16 in function hdlc_rx_done,
because bd_status register is 16bits
2. write bd_length register before writing bd_status register

Signed-off-by: Zhao Qiang <qiang.zhao@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>