phy: dm816x: use __maybe_unused to hide pm functions

The dm816x USB PHY driver uses UNIVERSAL_DEV_PM_OPS to access
its suspend/resume functions, which causes a warning about
unused symbols when CONFIG_PM is disabled:

drivers/phy/phy-dm816x-usb.c:121:12: error: 'dm816x_usb_phy_runtime_suspend' defined but not used [-Werror=unused-function]
drivers/phy/phy-dm816x-usb.c:139:12: error: 'dm816x_usb_phy_runtime_resume' defined but not used [-Werror=unused-function]

This adds __maybe_unused annotations to let the compiler know
it can silently drop the function definition.

Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/phy/phy-dm816x-usb.c

···
 	.owner		= THIS_MODULE,
 };
 
-static int dm816x_usb_phy_runtime_suspend(struct device *dev)
+static int __maybe_unused dm816x_usb_phy_runtime_suspend(struct device *dev)
 {
 	struct dm816x_usb_phy *phy = dev_get_drvdata(dev);
 	unsigned int mask, val;
···
 	return 0;
 }
 
-static int dm816x_usb_phy_runtime_resume(struct device *dev)
+static int __maybe_unused dm816x_usb_phy_runtime_resume(struct device *dev)
 {
 	struct dm816x_usb_phy *phy = dev_get_drvdata(dev);
 	unsigned int mask, val;