usb: hide unused usbfs_notify_suspend/resume functions

The declaration is in an #ifdef, which causes warnings when building
with 'make W=1' and without CONFIG_PM:

drivers/usb/core/devio.c:742:6: error: no previous prototype for 'usbfs_notify_suspend'
drivers/usb/core/devio.c:747:6: error: no previous prototype for 'usbfs_notify_resume'

Use the same #ifdef check around the function definitions to avoid
the warnings and slightly shrink the USB core.

Fixes: 7794f486ed0b ("usbfs: Add ioctls for runtime power management")
Signed-off-by: Arnd Bergmann <[e-mail]>
Reviewed-by: Sebastian Reichel <[e-mail]>
Acked-by: Alan Stern <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/core/devio.c

···
 	return 0;
 }
 
+#ifdef CONFIG_PM
 /* The following routines apply to the entire device, not interfaces */
 void usbfs_notify_suspend(struct usb_device *udev)
 {
···
 	}
 	mutex_unlock(&usbfs_mutex);
 }
+#endif
 
 struct usb_driver usbfs_driver = {
 	.name =		"usbfs",