tty: serial: msm_serial: Add __maybe_unused to suspend/resume callbacks

As stated under "20) Conditional Compilation" in coding-style.rst. We
shall rather use __maybe_unused than preprocessor macros in such cases.
Signed-off-by: Pascal Huerst <pascal.huerst@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/msm_serial.c

@@ -1812,8 +1812,7 @@ static const struct of_device_id msm_match_table[] = {
 };
 MODULE_DEVICE_TABLE(of, msm_match_table);
 
-#ifdef CONFIG_PM_SLEEP
-static int msm_serial_suspend(struct device *dev)
+static int __maybe_unused msm_serial_suspend(struct device *dev)
 {
 	struct msm_port *port = dev_get_drvdata(dev);
 
@@ -1822,7 +1821,7 @@ static int msm_serial_suspend(struct device *dev)
 	return 0;
 }
 
-static int msm_serial_resume(struct device *dev)
+static int __maybe_unused msm_serial_resume(struct device *dev)
 {
 	struct msm_port *port = dev_get_drvdata(dev);
 
@@ -1830,7 +1829,6 @@ static int msm_serial_resume(struct device *dev)
 
 	return 0;
 }
-#endif /* CONFIG_PM_SLEEP */
 
 static const struct dev_pm_ops msm_serial_dev_pm_ops = {
 	SET_SYSTEM_SLEEP_PM_OPS(msm_serial_suspend, msm_serial_resume)