phy: tegra: xusb: mark PM functions as __maybe_unused

When these are not referenced, gcc prints a harmless warning:

drivers/phy/tegra/xusb.c:1286:12: error: 'tegra_xusb_padctl_resume_noirq' defined but not used [-Werror=unused-function]
 1286 | static int tegra_xusb_padctl_resume_noirq(struct device *dev)
      |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/phy/tegra/xusb.c:1276:12: error: 'tegra_xusb_padctl_suspend_noirq' defined but not used [-Werror=unused-function]
 1276 | static int tegra_xusb_padctl_suspend_noirq(struct device *dev)
      |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: c545a905 ("phy: tegra: xusb: Add sleepwalk and suspend/resume")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20210721152550.2976003-1-arnd@kernel.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/phy/tegra/xusb.c

@@ -1273,7 +1273,7 @@ static int tegra_xusb_padctl_remove(struct platform_device *pdev)
 	return err;
 }
 
-static int tegra_xusb_padctl_suspend_noirq(struct device *dev)
+static __maybe_unused int tegra_xusb_padctl_suspend_noirq(struct device *dev)
 {
 	struct tegra_xusb_padctl *padctl = dev_get_drvdata(dev);
 
@@ -1283,7 +1283,7 @@ static int tegra_xusb_padctl_suspend_noirq(struct device *dev)
 	return 0;
 }
 
-static int tegra_xusb_padctl_resume_noirq(struct device *dev)
+static __maybe_unused int tegra_xusb_padctl_resume_noirq(struct device *dev)
 {
 	struct tegra_xusb_padctl *padctl = dev_get_drvdata(dev);