staging/rtl8192u - check for skb alloc failure

It's possible for dev_alloc_skb() to fail. Propagate the error to the caller,
so it can clean up and drop the packet. The sender should end up retransmitting
the packet, hopefully at a time we're prepared to allocate skb's again.
Reported-By: Nicholas Krause <xerofoify@gmail.com>
Signed-Off-By: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8192u/ieee80211/ieee80211_rx.c

@@ -847,6 +847,8 @@ static u8 parse_subframe(struct sk_buff *skb,
 #else
 			/* Allocate new skb for releasing to upper layer */
 			sub_skb = dev_alloc_skb(nSubframe_Length + 12);
+			if (!sub_skb)
+				return 0;
 			skb_reserve(sub_skb, 12);
 			data_ptr = (u8 *)skb_put(sub_skb, nSubframe_Length);
 			memcpy(data_ptr, skb->data, nSubframe_Length);