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>
diff --git a/drivers/serial/timbuart.c b/drivers/serial/timbuart.c
index 3d40be6..34b31da0 100644
--- a/drivers/serial/timbuart.c
+++ b/drivers/serial/timbuart.c
@@ -231,7 +231,7 @@
 		iowrite32(CTS_DELTA, port->membase + TIMBUART_ISR);
 		cts = timbuart_get_mctrl(port);
 		uart_handle_cts_change(port, cts & TIOCM_CTS);
-		wake_up_interruptible(&port->state->delta_msr_wait);
+		wake_up_interruptible(&port->state->port.delta_msr_wait);
 	}
 
 	*ier |= CTS_DELTA;