rt2x00: fix rmmod crash

Avoid queue and run autowakeup_work when device is not present anymore.
That prevent rmmod and device remove crash introduced by:

commit 1c0bcf89d85cc97a0d9ce4cd909351a81fa4fdde
Author: Ivo van Doorn <ivdoorn@gmail.com>
Date:   Sat Apr 30 17:18:18 2011 +0200

    rt2x00: Add autowake support for USB hardware

Signed-off-by: Stanislaw Gruszka <stf_xl@wp.pl>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/rt2x00/rt2x00config.c b/drivers/net/wireless/rt2x00/rt2x00config.c
index 555180d..b704e5b 100644
--- a/drivers/net/wireless/rt2x00/rt2x00config.c
+++ b/drivers/net/wireless/rt2x00/rt2x00config.c
@@ -250,7 +250,8 @@
 	if (ieee80211_flags & IEEE80211_CONF_CHANGE_CHANNEL)
 		rt2x00link_reset_tuner(rt2x00dev, false);
 
-	if (test_bit(REQUIRE_PS_AUTOWAKE, &rt2x00dev->cap_flags) &&
+	if (test_bit(DEVICE_STATE_PRESENT, &rt2x00dev->flags) &&
+	    test_bit(REQUIRE_PS_AUTOWAKE, &rt2x00dev->cap_flags) &&
 	    (ieee80211_flags & IEEE80211_CONF_CHANGE_PS) &&
 	    (conf->flags & IEEE80211_CONF_PS)) {
 		beacon_diff = (long)jiffies - (long)rt2x00dev->last_beacon;