serial: mrst_max3110: Check the irq number before enable/disabe irq in PM hooks

We should check the validity of the irq number before calling
disable_irq() and enable_irq() in the suspend/resume function,
as "max->irq == 0" means the irq is not enabled for max3110
device, otherwise it will hurt device whose irq number is really 0.
Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/mrst_max3110.c

@@ -749,6 +749,7 @@ static int serial_m3110_suspend(struct device *dev)
 	struct spi_device *spi = to_spi_device(dev);
 	struct uart_max3110 *max = spi_get_drvdata(spi);
 
+	if (max->irq > 0)
 		disable_irq(max->irq);
 	uart_suspend_port(&serial_m3110_reg, &max->port);
 	max3110_out(max, max->cur_conf | WC_SW_SHDI);
@@ -762,6 +763,7 @@ static int serial_m3110_resume(struct device *dev)
 
 	max3110_out(max, max->cur_conf);
 	uart_resume_port(&serial_m3110_reg, &max->port);
+	if (max->irq > 0)
 		enable_irq(max->irq);
 	return 0;
 }