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/pmac_zilog.c b/drivers/serial/pmac_zilog.c
index 0dc7868..0700cd1 100644
--- a/drivers/serial/pmac_zilog.c
+++ b/drivers/serial/pmac_zilog.c
@@ -369,7 +369,7 @@
 			uart_handle_cts_change(&uap->port,
 					       !(status & CTS));
 
-		wake_up_interruptible(&uap->port.state->delta_msr_wait);
+		wake_up_interruptible(&uap->port.state->port.delta_msr_wait);
 	}
 
 	if (status & BRK_ABRT)