Bluetooth: hci_uart: check the return value of recv()

Check the return value of hu->proto->recv() in hci_uart_tty_receive()
the recv() may return error, check it, not add this to statistics.

Signed-off-by: Jiejing Zhang <jiejing.zhang@freescale.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>