usb: ehci: unlink_empty_async_suspended() only used with CONFIG_PM

Compiling with !CONFIG_PM generates an unused function warning on
unlink_empty_async_suspended().

Enclose the function in a #ifdef CONFIG_PM
Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ehci-q.c

@@ -1293,6 +1293,7 @@ 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)
 {
@@ -1305,6 +1306,7 @@ 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 */