serial: move delta_msr_wait into the tty_port

This is used by various drivers not just serial and can be extracted
as commonality

Signed-off-by: Alan Cox <alan@linux.intel.com>

drivers/serial/amba-pl010.c

@@ -225,7 +225,7 @@ static void pl010_modem_status(struct uart_amba_port *uap)
 	if (delta & UART01x_FR_CTS)
 		uart_handle_cts_change(&uap->port, status & UART01x_FR_CTS);
 
-	wake_up_interruptible(&uap->port.state->delta_msr_wait);
+	wake_up_interruptible(&uap->port.state->port.delta_msr_wait);
 }
 
 static irqreturn_t pl010_int(int irq, void *dev_id)