[Blackfin] serial driver: fix bug - should not wait for the TFI bit, just clear it when tx stop.

Signed-off-by: NSonic Zhang <sonic.zhang@analog.com>
Signed-off-by: NBryan Wu <bryan.wu@analog.com>

drivers/serial/bfin_5xx.c

@@ -95,9 +95,6 @@ static void bfin_serial_stop_tx(struct uart_port *port)
 	disable_dma(uart->tx_dma_channel);
 #else
 #ifdef CONFIG_BF54x
-	/* Waiting for Transmission Finished */
-	while (!(UART_GET_LSR(uart) & TFI))
-		continue;
 	/* Clear TFI bit */
 	UART_PUT_LSR(uart, TFI);
 	UART_CLEAR_IER(uart, ETBEI);