mac80211: make sure hw_key exists before checking its flags

Fixes a bug introduced in:

commit 077a9154898b374f20555adc3f620cccd02581d6
Author: Arik Nemtsov <arik@wizery.com>
Date:   Sun Oct 23 08:21:41 2011 +0200

Reported-by: Arend van Spriel <arend@broadcom.com>
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/wpa.c

@@ -415,7 +415,8 @@ static int ccmp_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 	memmove(pos, pos + CCMP_HDR_LEN, hdrlen);
 
 	/* the HW only needs room for the IV, but not the actual IV */
-	if (info->control.hw_key->flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE)
+	if (info->control.hw_key &&
+	    (info->control.hw_key->flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE))
 		return 0;
 
 	hdr = (struct ieee80211_hdr *) pos;