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/sa1100.c b/drivers/serial/sa1100.c
index 61ef3ae..7f5e268 100644
--- a/drivers/serial/sa1100.c
+++ b/drivers/serial/sa1100.c
@@ -117,7 +117,7 @@
 	if (changed & TIOCM_CTS)
 		uart_handle_cts_change(&sport->port, status & TIOCM_CTS);
 
-	wake_up_interruptible(&sport->port.state->delta_msr_wait);
+	wake_up_interruptible(&sport->port.state->port.delta_msr_wait);
 }
 
 /*