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: c545a9056712 ("phy: tegra: xusb: Add sleepwalk and suspend/resume")
Signed-off-by: Arnd Bergmann <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/phy/tegra/xusb.c

···
 	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);
 
···
 	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);