staging/wlan-ng: Fix 'Branch condition evaluates to a garbage value' in p80211netdev.c

clang/scan-build complains that:
p80211netdev.c:451:6: warning: Branch condition evaluates to a garbage
value
        if ((p80211_wep.data) && (p80211_wep.data != skb->data))
	            ^~~~~~~~~~~~~~~~~

This can happen in p80211knetdev_hard_start_xmit if
- if (wlandev->state != WLAN_DEVICE_OPEN) evaluates to true.
the execution flow then continues at the 'failed' label where
p80211_wep.data is used without being initialized first.

-> Initialize the data field to NULL to fix this issue.
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wlan-ng/p80211netdev.c

@@ -351,6 +351,8 @@ static int p80211knetdev_hard_start_xmit(struct sk_buff *skb,
 	union p80211_hdr p80211_hdr;
 	struct p80211_metawep p80211_wep;
 
+	p80211_wep.data = NULL;
+
 	if (skb == NULL)
 		return NETDEV_TX_OK;