usb: ehci: mark unlink_empty_async_suspended() as __maybe_unused

Patch 4d053fda "usb: ehci: unlink_empty_async_suspended() only used
with CONFIG_PM" tried to hide the unlink_empty_async_suspended function
inside of an #ifdef to work around an unused function warning.

Unfortunately that had the effect of introducing a new warning:

drivers/usb/host/ehci-q.c:1297:13: warning: 'unlink_empty_async_suspended'
	declared 'static' but never defined [-Wunused-function]

While we could add another #ifdef around the function declaration to avoid
this, a nicer solution is to mark it as __maybe_unused, which will let
gcc silently drop the function definition when it is not needed.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ehci-q.c

@@ -1293,9 +1293,8 @@ static void unlink_empty_async(struct ehci_hcd *ehci)
 	}
 }
 
-#ifdef CONFIG_PM
 /* The root hub is suspended; unlink all the async QHs */
-static void unlink_empty_async_suspended(struct ehci_hcd *ehci)
+static void __maybe_unused unlink_empty_async_suspended(struct ehci_hcd *ehci)
 {
 	struct ehci_qh		*qh;
 
@@ -1306,7 +1305,6 @@ static void unlink_empty_async_suspended(struct ehci_hcd *ehci)
 	}
 	start_iaa_cycle(ehci);
 }
-#endif
 
 /* makes sure the async qh will become idle */
 /* caller must own ehci->lock */