ar9170: fix build when !CONFIG_PM

Fix this build error when CONFIG_PM is not set:
drivers/net/wireless/ath/ar9170/usb.c: In function 'ar9170_usb_probe':
drivers/net/wireless/ath/ar9170/usb.c:692:
	error: 'struct usb_device' has no member named 'reset_resume'
Signed-off-by: NAlexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ar9170/usb.c

@@ -689,7 +689,9 @@ static int ar9170_usb_probe(struct usb_interface *intf,
 	aru->common.exec_cmd = ar9170_usb_exec_cmd;
 	aru->common.callback_cmd = ar9170_usb_callback_cmd;
 
+#ifdef CONFIG_PM
 	udev->reset_resume = 1;
+#endif
 	err = ar9170_usb_reset(aru);
 	if (err)
 		goto err_freehw;