phy: twl4030: use __maybe_unused to hide pm functions

The twl4030 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-twl4030-usb.c:394:12: error: 'twl4030_usb_runtime_suspend' defined but not used [-Werror=unused-function]
drivers/phy/phy-twl4030-usb.c:408:12: error: 'twl4030_usb_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 <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/phy/phy-twl4030-usb.c

@@ -391,7 +391,7 @@ static void __twl4030_phy_power(struct twl4030_usb *twl, int on)
 	WARN_ON(twl4030_usb_write_verify(twl, PHY_PWR_CTRL, pwr) < 0);
 }
 
-static int twl4030_usb_runtime_suspend(struct device *dev)
+static int __maybe_unused twl4030_usb_runtime_suspend(struct device *dev)
 {
 	struct twl4030_usb *twl = dev_get_drvdata(dev);
 
@@ -405,7 +405,7 @@ static int twl4030_usb_runtime_suspend(struct device *dev)
 	return 0;
 }
 
-static int twl4030_usb_runtime_resume(struct device *dev)
+static int __maybe_unused twl4030_usb_runtime_resume(struct device *dev)
 {
 	struct twl4030_usb *twl = dev_get_drvdata(dev);
 	int res;