[SERIAL] Make port->ops constant

No one should write to the port->ops structure, so make it constant.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index 9437704..74142b7 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -1870,7 +1870,7 @@
 	mutex_lock(&state->mutex);
 
 	if (state->info && state->info->flags & UIF_INITIALIZED) {
-		struct uart_ops *ops = port->ops;
+		const struct uart_ops *ops = port->ops;
 
 		spin_lock_irq(&port->lock);
 		ops->stop_tx(port);
@@ -1932,7 +1932,7 @@
 	}
 
 	if (state->info && state->info->flags & UIF_INITIALIZED) {
-		struct uart_ops *ops = port->ops;
+		const struct uart_ops *ops = port->ops;
 		int ret;
 
 		ops->set_mctrl(port, 0);