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/sunzilog.c b/drivers/serial/sunzilog.c
index 055034d..ef693ae 100644
--- a/drivers/serial/sunzilog.c
+++ b/drivers/serial/sunzilog.c
@@ -451,7 +451,7 @@
 			uart_handle_cts_change(&up->port,
 					       (status & CTS));
 
-		wake_up_interruptible(&up->port.state->delta_msr_wait);
+		wake_up_interruptible(&up->port.state->port.delta_msr_wait);
 	}
 
 	up->prev_status = status;