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/sunsab.c b/drivers/serial/sunsab.c
index 7c4f2fe..d1ad341 100644
--- a/drivers/serial/sunsab.c
+++ b/drivers/serial/sunsab.c
@@ -297,7 +297,7 @@
 		up->port.icount.dsr++;
 	}
 
-	wake_up_interruptible(&up->port.state->delta_msr_wait);
+	wake_up_interruptible(&up->port.state->port.delta_msr_wait);
 }
 
 static irqreturn_t sunsab_interrupt(int irq, void *dev_id)