serial: mctrl_gpio: add IRQ locking

uart_handle_cts_change should be called with port->lock held. And for
this to be save you must also disable irqs.
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_mctrl_gpio.c

@@ -125,9 +125,12 @@ static irqreturn_t mctrl_gpio_irq_handle(int irq, void *context)
 	struct uart_port *port = gpios->port;
 	u32 mctrl = gpios->mctrl_prev;
 	u32 mctrl_diff;
+	unsigned long flags;
 
 	mctrl_gpio_get(gpios, &mctrl);
 
+	spin_lock_irqsave(&port->lock, flags);
+
 	mctrl_diff = mctrl ^ gpios->mctrl_prev;
 	gpios->mctrl_prev = mctrl;
 
@@ -147,6 +150,8 @@ static irqreturn_t mctrl_gpio_irq_handle(int irq, void *context)
 		wake_up_interruptible(&port->state->port.delta_msr_wait);
 	}
 
+	spin_unlock_irqrestore(&port->lock, flags);
+
 	return IRQ_HANDLED;
 }