blackfin: Fix tty compile error in PIO mode

Fixes this compile issue:

  drivers/serial/bfin_5xx.c: In function bfin_serial_rx_chars:
  drivers/serial/bfin_5xx.c:178: error: struct uart_info has no member named tty
Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/serial/bfin_5xx.c

@@ -174,10 +174,10 @@ static void bfin_serial_rx_chars(struct bfin_serial_port *uart)
 			return;
 		}
 
-	if (!uart->port.info || !uart->port.info->tty)
+	if (!uart->port.info || !uart->port.info->port.tty)
 		return;
 #endif
-	tty = uart->port.info->tty;
+	tty = uart->port.info->port.tty;
 
 	if (ANOMALY_05000363) {
 		/* The BF533 (and BF561) family of processors have a nice anomaly