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/serial_ks8695.c b/drivers/serial/serial_ks8695.c
index 4560b2e..2e71bbc 100644
--- a/drivers/serial/serial_ks8695.c
+++ b/drivers/serial/serial_ks8695.c
@@ -266,7 +266,7 @@
 	if (status & URMS_URTERI)
 		port->icount.rng++;
 
-	wake_up_interruptible(&port->state->delta_msr_wait);
+	wake_up_interruptible(&port->state->port.delta_msr_wait);
 
 	return IRQ_HANDLED;
 }