drivers/staging/wlan-ng/p80211conv.c: fixed a potential memory leak

Fixed a potential memory leak inside skb_ether_to_p80211()
	When the wep_encrypt() fails  the code return 2 directly
	Which causes the p80211_wep->data dangling

Add a kfree statement to reclaim that memory allocated

Signed-off-by: Lynn Lei <lynnl.yet@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>